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The American naturalist 



Essex Institute, American 

Society of Naturalists, JSTOR (Organization) 



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THE AMERICAN NATURAUST 



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THE 



AMERICAN NATURALIST 



A Monthly Journal 

Devoted to the Advancement of the Biological Sciences 

With Special Reference to the Factors of Evolution 



VOLUME XLVIII 



NEW YORK 
THE SCIENCE PRESS 

1914 



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PRESS OF 

THE NEW ERA PRINTINO COMPANY 

LANCASTER PA. 



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roi. zLTm, 10. MS jahiust, i>i4 



THE 

AMERICAN 
NATURALIST 



A M0HTEL7 JOXnUTAL 

Jtaroted to fhe AdTaneement of the Biological Scienoot witt 

Special Beforence to the Factors of Evolntioii 

OOVTBVTS 

Pa§€ 

I. A OeiMtte Analysli of th» Ohanf m produced by 8«loetloa la BxptrlsiMiU 

wltli TobMOO. Proftnor £. M. Eabt and H. K. Hatbs .... 5 

n. aynaadromorpboiu AnU, dMorlbod dnring tbe Dtcade, 1908-1918 

ProfeMor William Morton Whbelkb 49 

m. Sliorler ArttolM and Diiouitloa : 

On tbe Besnlts of Inbreeding a Mendellan Population — ^A Correction and Ex* 
tendon of Prerions Conclusions. Dr. Batmomd Pbarl— Isolati<m and Selec- 
tion allied in Principle. Dr. John T. Gulick - 07 



THE 80IEN0E FBE88 

IiAHOASTEB, PA. OABBI80H. H. T. 

■ZW 70BK: SVB-STAnOH M 



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The American Naturalist 



MSS Intended for poblioatfon and booke, etc., Intended for review ehoufd be 
sent to the Editor of THE AMERICAN NATURALIST, Garrlson-on- Hudson, New York. 

Short articles oontaining eommarlet of research work bearing on the 
probleas of organic evelntien are especially welcome, and will bo given preference 
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One hundreo reprints of contributions are supplied to authors firee of charge. 
Further reprints will be supplied at cost. 

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Canadian postage twenty-five cents additional. The charge fbr single copies is 
forty cents. The advertising rates are Four Dollars for a page. 

THE SCIENCE PRESS 

Lancaster, Pa. Qarrison, N. Y. 

NEW YORK : Sub-Station 84 

Bntored m teoond-elaai matter, April 2. 1906, at tht Post Offiet at Lancaitar, Pa., imder tbt At% of 

Congren of Mareh 8, 1879. 



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THE 

AMERICAN NATURALIST 



Vol. XLVni January, 19U No. 566 

A GENETIC ANALYSIS OF THE CHANGES PRO- 
DUCED BY SELECTION IN EXPERIMENTS 
WITH TOBACCO* 

PROFESSOR E. M. EAST and H. K. HAYES 
BussET Institution of Habvard Univebsitt 

The Problem 

In 1903 Johannsen announced that continued selection 
of the extreme values of certain quantitative characters 
in successive self-fertilized generations of a number of 
strains of beans had produced no changes in the mean 
values of the characters. He concluded that these par- 
ticular strains were homozygous for the gametic factors 
whose interaction resulted in the characters investigated, 
that these homozygous characters may be properly de- 
scribed by one or more gametic factors nonvariable in 
transmissible qualities and properties, and that the varia- 
tions observed in the characters of any single fraternity 
were due entirely to the action of environmental condi- 
tions during ontogeny and were not inherited. Funda- 
mentally, these conclusions were a recognition of the gen- 
eral value of Mendelian description for all forms of in- 
heritance through sexual reproduction, combined with an 

1 These inyestigations were conducted with funds furnished by the Con- 
necticut Agricultural Experiment Station from their Adams' appropria- 
tions, bj the Bureau of Plant Industry of the United States Department of 
Agriculture, and by the Bussey Institution of Harvard University, and the 
writers desire to take this opportunity of expressing their sincere appre- 
ciation of this hearty cooperation which made the work possible. 

5 



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6 THE AMERICAN NATURALIST [V0L.XLVIII 

admission of disbelief in the inheritance of ordinary 
adaptive changes. The latter conception was Weismann- 
ian in that all inherited variations were held to be changes 
in the germ cells. It was not necessary to suppose it im- 
possible for the environment to produce such changes and 
therefore to have been of no value during the course of 
evolution, but merely to suppose that during the compara- 
tively short period of experimental investigations no gam- 
etic variations have occurred traceable to such a cause. 
For his first conclusion to be justified, it was assumed that 
the changes which every biologist knows do follow the 
continuous selection of extremes under certain conditions 
are to be interpreted entirely by the segregation and re- 
combination of hypothetical gametic factors which are 
constant in their reactions under identical conditions. 

Numerous investigators working on ''pure lines" with 
different material corroborated Johannsen's conclusions, 
and, as it was seen to be possible to interpret in the same 
manner changes made by selection in experiments where 
self-fertilized lines were not used, such as those of the 
Vilmorins and others on sugar beets and those of the 
Illinois Agricultural Experiment Station on maize, many 
biologists accepted them and considered them a great ad- 
vance over former conceptions of the mechanism of 
heredity. On the other hand, there were those who main- 
tained a skeptical attitude, the chief criticism directed 
against the conception being that all progress due to 
selection must have a limit, which in many of these ex- 
periments had already been reached, and that even if re- 
sults were being obtained action might be too slow to be 
detected. 

The Material 

These criticisms were reasonable when applied to cer- 
tain specific cases, and in 1908 the experiments reported 
in this paper were designed with the hope of testing their 
validity, using the species ordinarily grown for commer- 
cial tobacco, Nicotiana tabacum, as the material. This 
plant satisfies the conditions which are requisite for 



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No. 565] CHANGES PRODUCED BY SELECTION 7 

material used in pure line studies. It has characters that 
can be estimated readily and accurately and which are 
affected only slightly by external conditions. It is easily 
grown, is naturally self -fertilized, reproduces prolifically, 
and is known in many markedly different varieties. In 
fact, it is an ideal subject for work of this kind. 

The investigations were not patterned after the stand- 
ard type set by Johannsen wherein the constancy of suc- 
cessive generations of pure lines grown from selected 
extremes were tested, since even if it were possible to 
gather a quantity of data at all comparable to that col- 
lected by Johannsen ( :09) and Jennings ( :08) in their 
brilliant investigations, the criticisms mentioned above 
might still be made. The plan chosen was that of cross- 
ing two varieties of tobacco which differed in a character 
complex easily and precisely determined, and of selecting 
extremes from a number of families of the F2 generation. 
If Johannsen 's views be incorrect, such continued selec- 
tion should affect each family in the same degree. If his 
conclusions be justified, selection should reach an end- 
poiat in different generations in different families, and 
there should be no relation between the number of genera- 
tions required to reach this end-point and the progress 
that is possible. 

There should be no need of a historical summary of the 
previous investigations that have been interpreted as cor- 
roborating or refuting Johannsen 's conclusions. Such 
summaries have been made in other papers. It should be 
mentioned, however, that the classical researches of Pearl 
(:11) on the inheritance of fecundity in the domestic 
fowl have been so planned and executed that certain of 
the criticisms directed against Johannsen mentioned above 
are not justified, yet Pearl finds himself thoroughly in 
accord with the Danish physiologist's position. 

Several hundred varieties of Nicotiana tahacum exist 
which differ from each other by definite botanical char- 
acters, yet only two general characters suitable for our 
purpose were found. We desired to confine our observa- 
tions to quantitative characters that were influenced but 



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8 



THE AMERICAN NATURALIST [Vol. XLVm 



little by environment, and number of leaves and size of 
corolla were the only ones that satisfied this requirement. 
Such character differences as height of plant and size of 
leaf, while undoubtedly transmissible, are influenced so 
strongly in their development by nutrition that work with 
them is exceedingly diflBcult. For example, if a certain 
variety of Nicotiana tahacum is grown under the best of 
field conditions, the longest leaves are about 28 inches and 
the total height about 6 feet, but a portion of the same 
seed fraternity may be grown to maturity in 4-inch pots 
without reaching a height of over 16 inches or having 
leaves longer than 4 inches. On the other hand, several 
experiments conducted in the same manner have shown 
no difference between the frequency curves of variation 
in number of leaves or of size of corolla, whether starved 
in small pots or grown under optimum conditions. The 
character complex number of leaves was chosen for this 
investigation rather than the size of corolla because vari- 
eties that differ greatly in number of leaves are common. 

TABLE I 

Frequency Distribution op Number op Leaves per Plant when 
Starved in Small Pots 

(Compare with frequency distribution under normal field conditions at 
Forest Hills, Massachusetts, in Tables VU and XI) 





No. of Lmtm per Plant 


Plant No. 


22 


28 


24 


25 


28 


27 


28 


29 


80 


81 


82 


83 


84 


80 


86 


87 


(6-l)-l 




2 

1 


3 
6 


10 
8 

1 


15 

15 



1 

12 

6 


8 
16 
8 

6 
10 


7 
12 

7 

1 

7 

13 


1 
5 
14 

2 
8 


































(e-2) 
(6-2)-2 

(se-i) 

(66-2) 


15 
2 


14 
3 


8 
12 


3 
17 


3 
16 














8 





1 




1 


4 


8 
4 




3 


1 















Previous Work of the '* Havana'' X *' Sumatra'' Cross 

Several crosses have been made between varieties of 
tobacco that had a mean difference of seven or eight 
leaves, but the majority of the data reported here were 
collected from the descendants of a cross made by A. D. 
Shamel between the types known in Connecticut as 
' * Havana ' ' and * ' Sumatra. ' ' The ' * Havana ' ' parent was 



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No. 565] CHANGES PRODUCED BY SELECTION 9 

from a variety that had been grown for a number of years 
at Granby, Connecticut. It averages about 20 leaves per 
plant although ranging from 16 to 25 leaves. The aver- 
age height is about 1.4 m. and the average leaf area about 
7 sq. dm. The *' Sumatra'' parent was a type specimen 
of a variety that had been introduced into Connecticut to 
be grown under cloth shade. It averages between 26 and 
27 leaves per plant with a range of from 21 to 32 leaves. 
The average height is nearly 2.0 m., but the average leaf 
area is only about 3 sq. dm. 

According to Shamel, the first hybrid generation of 
this cross developed somewhat more vigorously than the 
parent types and was uniform in its habit of growth. 
The second generation, he thought, was hardly more vari- 
able than the first. Several F3 families, the progeny of 
inbred F2 individuals, were grown in 1906 and proved to 
be a variable lot. One of these plants produced 26 small, 
round-pointed leaves with short intemodes between them. 
This plant was thought by Mr. E. Halladay, upon whose 
farm the experiment was conducted, and Mr. J. B. Stewart, 
of the U. S. Department of Agriculture, to be worth sav- 
ing from its promise of producing a desirable commercial 
type. 

In 1907 the Department of Agriculture made an agree- 
ment with Mr. Halladay to grow two acres of tobacco for 
experimental purposes, and on his own initiative Mr. 
Halladay grew a number of plants from inbred seed of 
the one that bore 26 leaves. This selection, numbered 2 
h-29 in accordance with the department nomenclature, 
was comparatively uniform in appearance and several 
plants were selfed. In Mr. Halladay 's absence, how- 
ever, all of the plants were ** topped,'' except one that 
happened to be rather late. This plant was selfed. It 
had 26 medium-sized, round leaves and grew to about the 
same height as the Connecticut Havana. 

In view of Mr. Halladay 's high opinion of the type, the 
seed of this plant and the remaining seed of its parent 
were planted in 1908. The plants of this generation pre- 
sented a uniform appearance and promised a high grade 



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10 THE AMERICAN NATURALIST [VoL.XLVra 

of wrapper tobacco, but the crop when cured lacked uni- 
formity. Some leaves of exceptionally high quality were 
produced, but the crop in general lacked that characteris- 
tic known as ^* grain'' and had too large a proportion of 
heavy leaves — the so-called *'tops." 

From this 1908 generation 100 seed plants were selfed, 
their leaves harvested, cured and fermented separately, 
and data on quality recorded. The type was also grown 
conunercially on a large scale. The commercial results, 
however, have been reported in another paper. We are to 
consider only the results gf the selection experiment that 
began in 1908, through the cooperation between the U. S. 
Department of Agriculture and the Connecticut Agricul- 
tural Experiment Station, a joining of forces that in 1909 
included the Bussey Institution of Harvard University. 
Shamel ( :07) considered the strain produced by this cross 
to be the result of a mutation. From a study of the 
data from the previous work on the cross it seemed to the 
writers that a different interpretation of the results might 
be made. While it was not impossible that the many- 
leaved type that had been isolated was the result of a 
mutation, it appeared much more probable that it had 
arisen through a recombination of Mendelian factors. 
The type had the habit of growth and size of leaf of the 
pure '* Havana" variety and the number of leaves of the 
''Sumatra" variety, a combination that might reason- 
ably be expected to be the result of the Mendelian law. 

Results on the Reciprocal Cross, ''Sumatra" 
X ^'Havana" 
To test the hypothesis that the new tobacco was the 
result of such recombination and could be reproduced 
whenever desired, the reciprocal of the original cross was 
made in 1910. The female parent, "Sumatra," was the 
direct descendant of a sister of the plant used as the 
male parent of the original cross by Shamel in 1903 
through seven generations of selfed plants. The male 
parent, "Havana," was from the commercial field of the 
Windsor Tobacco Growers' Corporation at Bloomfield, 



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No. 566] CHANGES PRODUCED BY SELECTION 1 1 

Connecticut. It was a descendant in a collateral line of 
the plant used by Shamel in 1903 as the female parent in 
his cross. 

Table n, giving the frequency distribution for the num- 
ber of leaves of the two parents and the first and the 
second hybrid generations, is a complete justification of 
our prediction as to how the hybrid type produced by 
Shamel originated. The ** Sumatra" and the F^ genera- 
tion were grown at New Haven, Connecticut, in 1911, the 
*' Havana" was grown at Bloomfield, Connecticut, in 1911 
from conmaercial seed of the same variety as the plant 
used for the male parent, while the Fg generation was 
grown at New Haven, Connecticut, in 1912. The F, gen- 
eration, producing an average of 23.3 ±: .14 leaves per 
plant, is intermediate in leaf number, since the * * Havana ' ' 
variety shows an average leaf number per plant of 19.8 
± .08 and the *^ Sumatra" variety 26.5 ±: .11. The varia- 
tion as determined by the coeflBcient of variability is some- 
what less for the F^ than for either parent. The value 
for the ** Sumatra" variety is 6.64 per cent. ±.28 per 
cent, for the ** Havana" variety 6.98 per cent. ±: .27 per 
cent, and for the F^ generation 6.24 per cent. ± .41 per 
cent. Taking into consideration the probable error in 
each case, one may say that the variability of the three 
populations is almost the same. 

The variability of the F2 generation, however, is greatly 
increased. This is shown by the high coefficient of vari- 
ability, 10.29 ±: .23 per cent., although a glance at the fre- 
quency distribution with its range of from 18 to 31 leaves 
brings home the point without recourse to biometrical 
calculation. 

The appearance of the plants in the field corroborated 
the data of Table II in other characters. The Fi genera- 
tion was intermediate in the various leaf characters, such 
as shape, size and texture, that distinguish '* Sumatra" 
from * * Havana ' ' tobacco, and in these characters it seemed 
as uniform as either of the parental varieties. On the other 
hand, the Fg generation was extremely variable. Some 
plants could not be distinguished from the pure *'Suma- 



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12 THE AMERICAN NATURALIST [VoL-XLVm 

tra,'' others resembled ** Havana/' although of course the 
majority were intermediate in various degrees. Several 
plants combined the leaf size and habit of growth of the 
** Havana" parent with the leaf number of the ** Suma- 
tra'' parent. In other words, plcmts were produced in 
the F2 generation by the recombination of Mendelian fac- 
tors that exactly repeated the type which Shamel had ob- 
tained in the F^ generation of the reciprocal cross made 
in 1903 and which he thought was due to a mutation. 
This fulfilled adequately the prediction made by us in 
1908. 

Results of Selecting fob High Numbeb and Low Num- 
ber OF Leaves in the ** Havana" X ** Sumatra" 

Cross 

Li describing the reproduction of Shamel 's hybrid with 
numerous large leaves by a reciprocal cross, there has 
been a chronological inversion. This was done simply to 
show that the original hybrid known commercially as 
**The Halladay" was actually a recombination of Men- 
delian factors in which the ** Havana" and the ** Suma- 
tra" varieties differed. We will now describe the effects 
of selection on the original '* Halladay hybrid." 

It wiU be recalled that the selection experiment which 
is the principal subject of this paper began with the self- 
ing of 100 seed plants of Shamel's Halladay hybrid in 
1908. These plants were the F4 and F^ generations of the 
cross ''Havana" X ''Sumatra." Plants numbered from 
1 to 49 were the F4 generation ; those numbered from 50 
to 100 were the F5 generation. They were apparently 
breeding true for the short habit of growth and large- 
sized leaf of the "Havana" parent and the goodly num- 
ber of leaves of the "Sumatra" parent. The casual ob- 
server either would have said with Shamel that here was 
a mutation breeding as true as any tobacco variety, or 
that a fixed hybrid, a hybrid homozygous in all of its 
gametic factors, had been produced. Accurate data 
taken on the progeny of those of the F4 and Fg seed plants 
which it was possible for us to grow in our limited space, 



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No. 565] CHANGES PRODUCED BY SELECTION 13 

however, show that such judgments would have been 
superficial. The general type of the plant did appear to 
be fixed, but the frequency distribution for number of 
leaves of the F^ and F^ populations were not the same. 
Strictly speaking, they were not fixed. What would be 
the result of selecting (and selfing) extremes from these 
ddflferent families for a number of years? A tentative 
answer to this question is to be obtained by examining 
the remainder of our tables. 

The tables are arranged roughly in the order of the 
effect that selection has had in changing the mean of the 
various families that were the starting points of this part 
of the experiment. The selections were grown near Bloom- 
field, Connecticut, on the light sandy loam of that region, 
soil typical of that which produces the famous Connecti- 
cut River Valley wrapper tobacco. Duplicate experi- 
ments with several of the original families were made at 
New Haven, Connecticut, however, on an impoverished 
soil not fitted to grow a good quality of tobacco even after 
supplying large quantities of tobacco fertilizer, and in 
the condition used not fitted to grow good crops of any 
kind. Two families were also grown in triplicate, the 
third selections being planted at Forest Hills, Massachu- 
setts, on a very fine type of rich garden land which brought 
out maximum luxuriance of growth, but which did not 
produce good tobacco quality. These experiments were 
not true repetitions of the experiments at Bloomfield, 
Connecticut, since aliquot portions of the seed from the 
selfed plant grown there were not sent to the other places 
to be grown. But they were duplicates in that each 
family came from the same F4 or Fg mother plant, 
although, beginning with the Fg or Fe population, differ- 
ent selfed seed plants furnished the starting point of selec- 
tions carried on independently. In this way there were 
afforded a greater number of chances to see what selec- 
tion could do. 

Table III shows the results obtained from family No. 
77. This family arose from an F5 plant having 23 leaves, 
one below the modal leaf number if we may juTJge from 



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14 



THE AMERICAN NATURALIST [Vol. XLVTEI 






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16 THE AMERICAN NATURALIST [VoL.XLVin 

the F2 generation of the reciprocal cross where the mode 
was at 24 to 25 leaves. The F^ fraternity that it pro- 
duced was somewhat smaller than one would wish if 
he were to be confident of the calculations made. The 
mode is 22 leaves and the mean nearly the same, 22.4 
± .11 leaves. From among these plants, a minus variant 
having 20 leaves and a plus variant having 27 leaves were 
selected to produce the F^ generation. The modes in this 
generation are 21 and 25 leaves, respectively, a difference 
of 4 leaves ; and the means are 21.9 ± .08 and 24.9 ± .11 
leaves, respectively, a difference of 3 leaves. Progress in 
both directions continued when a 20-leaved plant was 
selected to carry on the minus strain, and a 30-leaved 
plant was selected to carry on the plus strain. The modal 
classes of the Fg generation are 21 leaves in the minus 
selection and 26 leaves in the plus selection, while the 
means are 21.3 ±: .05 leaves and 26.6 ± .07 leaves, respect- 
ively. In the Fg generation the plus selection was lost, 
but the minus selection grown from a 20-leaved plant had 
the mode dropped to 18 leaves and the mean to 18.4 ± .08 
leaves. In order not to lose the plus selection entirely, 
however, more of the Fg generation seed was grown in 
1912. The mode is the same as in 1911, but the mean 
dropped slightly to 25.8 ±: .08 leaves. 

Here one notices what is very common throughout the 
experiment ; the extremes selected for mother plants were 
not members of the most extreme classes. This means 
simply that vigorous healthy specimens were always 
selected as the mother plants, and often the most extreme 
variants did not come up to the standard. It is hardly 
just to criticize this procedure, however, for with the best 
care that it was possible to give, the experiments with 
several families were terminated on account of non- 
germination of seed or for some similar reason, it being 
impossible, on account of the pressure of other work, to 
self many plants in each selection. Even where seed 
from several mother plants was collected, it did not in- 
sure the continuation of that selection. The necessary 
space and care involved in growing so many seedlings in 



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18 THE AMERICAN NATURALIST [Voi^XLVni 

isolated seed pans filled with sterilized soil made it im- 
possible to start more than two sets of plants for each 
plus and each minus selection. Generally both sets grew 
perfectly, but occasionally both failed, and in that case it 
was usually too late in the season to start a third set even 
if it were available. 

The second part of Table III shows the results obtained 
on the poor soil of New Haven, Connecticut, with the same 
family. There was continuous progress in both direc- 
tions. The minus selections during the three generations 
show a constant reduction of mode, the figures being 23, 
22 and 21; the plus selections show an even greater in- 
crease in mode, the figures being 25, 27 and 28. The same 
decrease and increase occur in the means until in the F^ 
generation there is a difference of nearly 9 leaves, the cal- 
culated means being 20.9db.08 leaves and 29.7±.14 leaves, 
respectively. 

Figs. 1 and 2 show typical plants of the plus and minus 
strains of this family as developed by 3 years of selection. 
Fig. 3 illustrates an interesting change of phyllotaxy in 
some plants of (77--2)-l-l as grownat New Haven in 1912. 

Passing to the data on Family No. 76 (Table IV) there 
is the same evidence of the effectiveness of selection, ex- 
cluding the minus strain in 1910, of which only 31 plants 
were healthy. This effect is markedly less than with the 
other family. The mode of the minus selection remained 
at 24 leaves and the mean was reduced only from 24.1 
± .11 leaves to 23.9 ± .05 leaves, — hardly a significant 
figure. The mode of the plus selection crept up to 26-27 
and the mean to 26.9 ± .07 leaves, there being here one 
more generation than in the case of the minus strain. 

Table V gives the data on plus and minus selections of 
Family No. 19 at Bloomfield for two generations. The 
original family stock of the Fg generation has the mode at 
27 leaves and the mean at about 26 leaves. A 24-leaved 
plant of this generation became the parent of the minus 
strain, giving in the Fe generation a population with the 
same mode and a slightly higher mean (26.9 ± .08 leaves). 
Continuation of the strain through a 24-leaved plant gave 



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No. 565] CHANGES PRODUCED BY SELECTION 



19 



an F7 population with the mode one class lower and the 
mean at 25.8 db .09 leaves. Whether this slight reduction 
really means anything we are unable to say. At least, if 
it yields at all to selection, 
the progress is very slow. 
On the other hand, a con- 
siderable gain has been 
made in the plus selec- 
tions. The mode rose im- 
mediately to 29 leaves 
when the progeny of a 29- 
leaved plant were grown, 
and went up to 30 leaves 
the next generation, the 
modal condition being the 
same as the number of 
leaves of the parent plant. 
The means are 26.3db.l0 
leaves, 28.7 d= .10 leaves 
and 29.2 it .08 leaves, the 
amount of progress being 
— as may be seen — 2.4 
leaves and 0.5 leaf in the 
two successive genera- 
tions. This result appar- 
ently indicates a slowing 
down of the effect of selec- 
tion. 

The continuation of the 
table gives the results ob- 
tained at New Haven on 
this same family. Here 
there are data from three 
generations, and these 
data modify the conclu- 
sions based on the results 

obtained at Bloomfield. Both plus and minus strains 
nearly parallel the Bloomfield results for two generations. 



Fig. 1. Plant op Halladat Ha- 
vana Tobacco (77-2) -1-1, which Av- 
BBAOES 29.7 Leaves Psb Plant. It 
IS THB Result of Three Ybabs of Se- 
lection FOB High Leaf Numbeb in 
Family 77, which Averaged 22.4 
Leaves Per Plant in 1909. New 
Haven, 1912. 



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20 THE AMERICAN NATURALIST [VoL.XLVra 

the F7 generation means being 28.3 ± .11 leaves and 25.1 
± .15 leaves, respectively, but in the Fg generations they 
differ. Selecting minus extremes for the first two genera- 



no. 2. Plant or Halladat Havana Tobacco (77-1) -1-1, which Atbsaobs 
20.9 LSAYBS PiB Plant. It is thb Rbsui^t of Thbbb Ybajis or Sblbction fob 
Low Lbat Numbbb in Family 77. Nbw Havbn, 1912. 

tions reduced the mean of that line from 26.3 ± .10 leaves 
to 25.1 ± .15 leaves, but the third selected generation (Fg) 
had a higher mean than the original family (27.3 ± .08 
leaves) . The parent plant of this Fj generation produced 



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No. 666] CHANGES PRODUCED BY SELECTION 21 

24 leaves, and as the strain indicated that it was hetero- 
zygous for a number of factors by showing a coeflScient of 
variability of 8.29 d= .42 per cent-, it is possible that the 
selected parent plant may have belonged gametically to a 
higher class than was indicated somatically; nevertheless, 
it can not be denied that three generations of selected 
minus extremes have produced no results. This conclu- 
sion is not valid for the plus strain. Starting with 26.3 ±. 
.10 as the mean number of leaves (Fg) , the succeeding gen- 
erations had means of 27.1 it .07 leaves, 28.3 dz .11 leaves 
and 30.0 it .11 leaves. The differences are 0.8, 12 and 1.7 
leaves, respectively. Progressive change has certainly f ol- 



Fio. 8. Chanob of Phyllotaxy in Some Plants of (77-2) -1-1 Grown in New 

Haven in 1912. 



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22 



THE AMEBIC AN NATURALIST [Vol. XLVin 



lowed, and unless one considers that the results of 1912 are 
somewhat too high (probably a valid assumption), the 
change has increased instead of decreased. Naturally 
there must be a decreased momentum in change of mean 
time, but this decrease is not yet shown by the figures. 




Pig. 4. Plant op Halladay Ha- 
TANA Tobacco (19-2) -1-2, which Av- 
BSAOBS 30 Lbaves Peb Plant. It 
IS THB Rbsuivt of Thebb Ybabs of Sb- 
lbction fob hloh leaf numbeb in 
Family 19, which in 1909 Avebaqed 
26.3 Leaves Peb Plant. New Haven, 
1912. 



Fig. 5. Plant op Halladat Ha- 
vana Tobacco (19-1) -1-1, which Av- 
BBAGES 27.3 Leaves Peb Plant. Thbbb 
Ybabs of Selection fob Low Lbaf 
Numbbb Havb Pbovbd Unsuccessful. 
New Haven, 1912. 



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No. 565] CHANGES PRODUCED BY SELECTION 23 

Bepresentative plants of the plus and minus strains of 
family 19 as obtained by three years of selection at New 
Haven are shown in Figs. 4 and 5. 

Family No. 5 (Table VI) shows a decrease in mode 
from 28 to 26 leaves, and a similar decrease in mean from 
28.1 ±: .06 leaves to 26.6 ± .09 leaves as a result of the first 
minus selection. A second minus selection, however, in- 
dicates either that the future progress is to be very slow 
or that the entire effect of selection was manifested in the 
first selected generation. 

With the three parts of Table VH we take up the re- 
sults on Family No. 6 at all three stations. The minus 
strain was carried on only two generations at Bloomfield, 
but with this exception there are data upon three genera- 
tions. At Bloomfield the two generations of selected 
minus extremes resulted in 0.6 leaf decrease in the mean, 
but at New Haven the results were negative, the means 
advancing from 25.8 ±: .06 leaves to 27.9 zt .12 leaves in 
three generations, while at Forest Hill the mean remained 
practically the same. Surely selection was unprofitable 
here. 

The first year of selection from the other end of the 
curve, however, resulted in marked progress. The mean 
advanced nearly 5 leaves in each case. The original F5 
mean is 25.8 ±: .06 leaves, but the three Fe means are 30.7 
dz .09, 29.6 dt .08 and 30.8 zt .12 leaves. This is a remark- 
able concurrence of results. The means in the two suc- 
ceeding generations were about the same in the Bloomfield 
and New Haven experiments, but there was another defi- 
nite advance at Forest Hills. Such a result should not 
be unexpected. If the Fe generation were almost but not 
quite a homozygous lot, and if one assumes that selection 
of extremes from homozygous population has no effect 
in shifting the mean, it would frequently happen that 
some individuals selected to continue the line would be 
homozygous in all factors and some heterozygous in one 
or more factors. 

The cause of the peculiar distribution of the population 
(high variability) of the Fg generation grown in Bloom- 



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24 



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No. 565] CHANGES PRODUCED BY SELECTION 27 

field is not clear. It is possible that the plants having 
from 18 to 23 leaves were diseased, but no such condition 
could be recognized in the field. Again, it is possible 
that a few Havana plants were mixed in by mistake, 
although as the leaves of the selection are characteris- 
tically diflferent from Havana and as the plants with low 
leaf numbers resembled the remainder of the row, this 
supposition is improbable. The most likely explanation 
is that mutation occurred in a few gametes of the mother 
plant, a condition that did arise, or that we assume to 
have arisen, in Family 41 (see Table X). At any rate, 
the change did not follow the path of selection. 

In Figs. 6 and 7 are shown typical plants of Family No. 
6 obtained by three years of selection in the effort to pro- 
duce strains of high and low leaf number, respectively. 

Family No. 34 (Table VllI) is peculiar — although this 
is not the only time the phenomenon occurred — in that 
the Fg population grown from a 24-leaved F4 plant seems 
not to have given the true mean. Plants with a low num- 
ber of leaves (22 and 20) were selfed to carry on the 
minus strain, but both gave means higher than was shown 
by the Fg generation. Perhaps further selection will 
produce results, but the case is not a hopeful one. The 
only evidence for such an assumption is the increased 
mean of the F^ plus strain. If it is assumed that 24.0 is 
nearer the true mean of the F5 population than the 22.9 
actually calculated, then the jump to 27.0 =t .08 leaves in 
the F7 generation gives us a basis for expecting results in 
Fg in the minus strain. 

Nothing can be said as yet about the minus strain of 
Family No. 12 (Table IX), for it happened that the first 
selection was a complete failure. Six plants were ob- 
tained, but the lowest number of leaves was 29. One of 
these plants was selfed and gave an F^ population having 
a mean of 28.7 ±: .09 leaves. Unfortunately the selections 
from this fraternity did not germinate and in 1912 we had 
to fall back on the reserve seed from which the 1911 crop 
came. The crops of 1911 and 1912 are therefore dupli- 
cates. The plus strain made an advance from 24.5 ib .10 



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28 THE AMERICAN NATURALIST [VouXLVHI 

leaves to either 26.8 ±l .07 or 29.0 ± .08 leaves. The first 
advance is 1.6, the second 0.7. We can give no explana- 



FiG. 6. Plant op Halladay Havana Tobacco (6-2) -1-1, which AvERAass 80.2 
Lbaves Pub Plant. It is the Result op Thbeb Years op Selection fob High 

LlAF NUMBEB in FAMILT 6, WHICH AVERAGED 25.8 LEAVES PEB PLANT IN I909w 

Nbw Haven, 1912. 



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No. 565] CHANGES PRODUCED BY SELECTION 29 

tion of the failure of the results of 1911 and 1912 to dupli- 
cate. This is the greatest deviation obtained in the course 
of our experiments. The results of 1912 are probably 
too high. It is yet too early to say whether or not this 



FxQ. 7. PLANT ov Haklapat Hatana Tobacco (6-1) -1-1, which Atbbagu 27.9 
Lbatbs Pbb Plakt. Thbbb Ybabs ov Sblbction to Dbcrbase the Leaf Numbbb 

OP THIS TTFB HATB PBOTBD UNSDCCXSSFULb NBW HAYEN, 1912. 



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30 THE AMERICAN NATURALIST [Vol. XLVIII 

strain is decreasing in the average annual shift of the 
mean. 

Family No. 41 shown in Table X gave perhaps the most 
peculiar results of any of the selections. It may be that 
no great shifting of the mean toward the minus end of the 
curve should have been expected, because the minus 
mothers were each rather high in number of leaves. There 
was one with 25 leaves and one with 24 leaves. This was 
unfortunate, but was made necessary by the number of 
late and diseased (mosaic) plants in the selection. Never- 
theless, each of these plants was below the mean of the 
previous generation and if a marked change would have 
followed the selection of extreme individuals, some change 
should have followed the selections of the individuals that 
were the actual mothers. But in spite of this fact the 
mean persistently rose from 23.9 ± .07 leaves to 26.3 it .08 
leaves, then to 28.1 zb .07 leaves, although the duplicate of 
this selection grown in 1912 went down slightly to 27.4 
± .07 leaves. In the plus strain successive generations 
of mothers having 28 and 30 leaves caused a small upward 
shift of the mean ; it became first 25.7 ± .09 leaves then 
25.6 it .14 leaves, although the 1912 duplicate of the last 
population had a mean of 26.9 db .08 leaves. 

The extraordinary phenomenon to which we wish to 
call particular attention, however, is not this behavior of 
the minus and plus strains in the regular selection ex- 
periment, but rather the origin of a few-leaved strain 
from a single individual that appeared in the Fe genera- 
tion of the plus strain. Eeferring to the table, it will be 
seen that in this generation a 12-leaved plant appeared. 
This is really a peculiar phenomenon, for we had never 
before observed a normal 12-leaved plant among the many 
thousands that have come under our observation. They 
do not occur. In this population the plant with the next 
lowest numbers of leaves had 20 leaves, and in classes 20 
and 21 there was only a single plant of each. This 12- 
leaved plant was selfed and gave rise to a population 
ranging from 8 leaves to 30 leaves, and having a vari- 
ability of 23.50 per cent. ± .11 per cent. The mean of the 



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No. 565] CHANGES PRODUCED BY SELECTION 31 

distribution was 19.8 ±: .28 leaves. A 10-leaved plant of 
this lot was selfed and gave a progeny with a mean of 
17.9 ±L .08 leaves and a variability of 11.24 per cent. ±: .33 
per cent. What interpretation can be given these facts! 

We believe a distinct mutation occurred, a mutation 
different from those of DeVries. At least DeVries be- 
lieves that the mutations that he has observed always 
breed true. If the following hypothesis as to the origin 
of the 12-leaved plant be true, it is unnecessary to sup- 
pose with DeVries that mutations always breed true or 
even that they often breed true. Of course DeVries be- 
lieves that his (Enothera mutations obey laws different 
from those of whose mechanism we know a little. He be- 
lieves that species crosses always breed true; that they 
do not Mendelize. This belief we hold to be unfounded. 
Species crosses have never been shown to breed true. 
There have been statements to the effect that crosses be- 
tween Rubiis species breed true, but no good evidence has 
been submitted in their support ; while the data of Tam- 
mes ( :11) on Linum species crosses, Davis ( :21) on (Eno- 
thera species crosses, and of East ( :13) on Nicotiana 
species crosses, concur in showing that species as well as 
varieties obey MendePs Law of segregation and recom- 
bination. Furthermore, we think that Heribert-Nilsson's 
(:12) beautiful experiments on DeVries *s own material 
show that the latter did not collect suflSciently exact data 
on his own crosses to find out whether they bred true or 
not. 

If one is to believe that a mutation in a hermaphroditic 
plant breeds true he must suppose that constitutional 
changes occur both in the male and the female gam- 
etes, or that the change occurs after fertilization. But it 
seems more probable that such a change will take place 
either in the one or the other gamete and not in both. This 
we believe to be the explanation of the appearance of the 
12-leaved tobacco plant. A mutation occurred in either 
an egg cell or a pollen cell. It does not matter in which 
one it is assumed because there is no evidence favoring 
either case to the exclusion of the other. This cell with 



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32 



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34 THE AMERICAN NATURALIST [Vol. XLVTEI 

a changed gametic constitution, — a loss of gametic fac- 
tors, — was fertilized by an unchanged cell. The un- 
changed cell may have had any of the gametic possibil- 
ities open to the germ cells of the 28-leaved plant of the 
Fg family in which the mutation arose, and we know that 
certain factors in this plant were heterozygous, for pro- 
gressive change followed the selection of a plus extreme 
in the next generation. The 12-leaved plant was there- 
fore a hybrid. It resulted from the union of a mutating 
germ cell of the mother plant that furnished the F^ gen- 
eration with an unchanged germ cell. We can even as- 
sume that the mutating germ cell, if fertilized by another 
of the same kind, would have produced a plant with less 
than 12 leaves. The reasons for believing this are simple. 
There is experimental evidence (Hayes, 1912) that the 
Fj generation of a cross between varieties differing in 
their number of leaves is intermediate in character. Our 
12-leaved plant is the lone representative of such an Fj 
generation. The Fg generation therefore should give 
plants with less than 12 leaves, and in fact such plants 
did occur. The distribution marked Fa in the table is 
the F2 generation, and this accounts for its extreme vari- 
ability. The distribution marked Fb is the Fg generation, 
and its variability is less than half that of the preceding 
generation. 

Family No. 56 was the second family to be grown at all 
three of the experimental statioiis (Table XI). It arose 
from a 26-leaved plant of the F5 generation which pro- 
duced an Fe progeny with a mean of 24.2 ± .06 leaves and 
a mode at 24 leaves. The three generations of the minus 
strain grown at Bloomfield remained practically the same. 
The last generation did indeed show a mean 1.0 leaf 
higher than the original population, but no dependence 
can be placed in data from only 25 plants. The data on 
the minus selections grown at New Haven are for this 
reason a little more dependable. They show a fluctuat- 
ing mean, but no progress due to selection, the F9 genera- 
tion having a little higher mean than the F^ generations. 
The three minus selections grown at Forest Hills also 



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No. 565] CHANGES PRODUCED BY SELECTION 35 

resulted in higher means, those for F^, Fg and F^ being 
25.3 It: .09, 26.0 ± .06 and 25.9 it .08 leaves, respectively. 

This peculiar result implies only that the mean of the 
original F^ population which was grown at Bloomfield 
was lower than it would have been if grown on the Forest 
Hills ^ soil. This is not a direct effect of environment on 
the growing plant. It has been shown conclusively in 
our pot experiments, as stated before, that starvation or 
optimum feeding has scarcely any effect on the number of 
leaves, although it has a marked effect on the develop- 
ment of many other characters. On the other hand, en- 
vironment does appear to have a marked effect on the 
number of leaves that a plant is to develop, if it acts 
during the development of the seed. It is well known by 
plant physiologists that the environment produces many 
of its effects very early in the life history of the indi- 
vidual or in the development of the organ concerned. For 
example, the so-called light leaves of the beech with two 
layers of palisade cells are differentiated from the shade 
leaves with only one row of palisade cells by the amount 
of light that falls on a branch during the season preceding 
the development of the leaves: that is, it is determined 
during the laying down of the bud from which the next 
season's growth of twig and leaves comes. This period 
during which a particular change is possible is called the 
critical i)eriod for that change by plant physiologists. 
Thus a plant may have hundreds of critical periods in its 
ontogeny, each marking an end-point of development be- 
yond which a certain feature is irrevocably fixed. For 
example, the critical period for that cell division that de- 
termines leaf size in the beech is much later than that 
which determines the number of layers of palisade cells. 

Now the critical period for influencing the number of 
leaves of the tobacco plant is practically at an end when 
the embryo plant goes into the resting stage of the seed. 
Before that time the number of leaves may be influenced 
by the external and the internal influences that form the 
total environment of the mother plant; after that time 
environment has little influence on the number of leaves. 



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36 THE AMERICAN NATURALIST [VoL-XLVHI 

The rise in the mean of the population of the Fg genera- 
tion of Family No. 56 is due partially to the effect of en- 
vironment, therefore, in that the mother plant was grown 
under better conditions, but is probably not to any great 
extent due to the conditions under which the plants them- 
selves were produced. 

The better environment of the mother plants does not 
account for all the rise in the means in populations Fg 
and Fg, but it accounts for part of it. It will be noticed 
that all of the populations grown at Forest Hills had 
higher means than those grown at Bloomfield and New 
Haven, although the Fe mother plants were grown at 
Bloomfield and not at Forest Hills. The greatest shift 
of the mean, however, comes in the Fg and Fg generations, 
for the mother plants of both of these populations were 
grown on the more fertile soil. There is a simple ex- 
planation of these facts, an explanation that is of great 
economic importance to practical tobacco growers. A 
part of the rise in mean at Forest Hills was due to set- 
ting the plants in the field there when they were in an 
earlier stage of development than those at Bloomfield and 
New Haven. They were not set earlier in the season (at 
least, one year they were set early, one year they were set 
at the average time and the third year they were set late), 
but they were set as small plants. When small plants 
(about 4 inches high) are set in the open the root system 
is equal to the task of supporting the aerial parts and the 
plants start right in to growing normally. There is no 
period of passivity. The plants produce leaves spaced 
with normal internodes and these leaves develop suffi- 
ciently to have a commercial value. But when the plants 
reach a height of 8 or 10 inches in the seed pans or seed 
beds and are then set in the field, the normal metabolism 
is likely to be upset for a time. The plant takes some 
time to recover its equilibrium and start a normal growth. 
During this period basal leaves begin to develop, but the 
internodes are so close together that they do not obtain 
their aliquot share of nutriment, hence they grow only to 
one quarter or one third their normal size and soon wither 



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No. 565] CHANGES PRODUCED BY SELECTION 



37 



and drop off. The leaf scars are left, but they are so 
close together that it is difficult to make a correct count of 
the number of leaves. But more important than this, 



Fio. 8. Plant of Hallaoat Ha- 
TANA Tobacco (56-2) -1-1, which Av- 
■BAGBS 27.6 Leaves Peb Plant. It 
IS THE Result of These Yeabs of Se- 
lection FOB High Leaf Numbbb in 
Family 56, which in 1900 Atebagbd 
24.2 Leaves Peb Plant. New Haven, 
1012. 



Fig. 9. Plant of Halladat Ha- 
vana Tobacco (56-1) -1-1, which Av- 
EBAOES 24.4 Leaves Peb Plant. Thbee 
Ybabs of Selection fob Low Leaf 
NuMBEB Have Pboved Unsuccessful, 
New Haven, 1912. 



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38 



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No. 565] CHANGES PRODUCED BY SELECTION 39 

the tobacco grower loses an average of from one to two 
of his most valuable leaves. 

The pins strain of Family No. 56, which we were dis- 
cussing when we digressed to speak of the critical periods 
of development, did show a considerable shifting of the 
mean following the selection of high-leaved mother plants. 
In the Bloomfield selections the mean went from 24.2 
di .06 to 26.7 ±z .08 leaves, then to 26.8 ± .07 leaves ; in the 
New Haven experiment the mean shifted to 27.4 ±.08 
leaves, — a gain of 3.2 leaves, — and then dropped to 26.4 
±.11 leaves, recovering again in the F^ generation to 
27.5 ± .11 leaves ; in the Forest Hills experiment the suc- 
cessive means were 27.2 ± .08, 28.9 ± .08 and 26.7 ± .06 
leaves. Summing up the data from this experiment, it 
may be assumed to be reasonably certain that no progress 
resulted from the selection of minus extremes, but that 
there was a slight effect gradually diminishing in quan- 
tity when plus extremes were selected. 

Bepresentative plants of Family 56 obtained by three 
years of selection in the effort to produce strains of high 
and low leaf number, respectively, are shown in Figs. 
8 and 9. 

Family No. K (Table XH) was grown on a farm near 
the Bloomfield experiments, in 1910. The records of the 
Fg generation consisted of the number of leaves of only 
31 plants. From among these individuals two plants 
were self ed to become the mothers of the Fe generation. 
Since no dependence can be placed on the Fj distribution 
by reason of the few plants and since it is not absolutely 
certain that the mother plants of Fe had 20 leaves each, 
the selection really began in 1911 with theF^ generation. 
There is a difference between the minus strain and the 
plus strain in 1911 and 1912, — 0.5 leaves the first year and 
1.3 leaves the second year, — ^however, so that one may 
assume the possibility of a slow shifting of the mean in 
both directions. 

The data on Family No. 73 are shown in Table XHI. 
This family came from a 28-leaved plant, one of the 
highest of the Fg generation. The Fe progeny of this 



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40 



THE AMERICAN NATURALIST [Vol. XLVIH 



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No. 565] CHANGES PRODUCED BY SELECTION 41 

individual showed a mean of 26.9 ± .06 leaves, and from 
among them plants having 25 and 29 leaves, respectively, 
were selected to start the minus and the plus lines. These 
two mother plants gave F7 populations alike as to mean, 
but differing by one class as to mode. The minus line 
had the higher mode. The extremes of this generation 
used in carrying on the experiment differed by 8 leaves, 
and the resulting progenies apparently followed the selec- 
tion. The means are 25.6 it .07 and 28.2 it .09 leaves. 
Whether these shifted means represent a permanent 
change or not we are not prepared to say. The minus 
mean is probably somewhere near the correct figure for 
in the Fg generation it was practically the same, but in 
the Fg generation of the plus strain the mean dropped 
from 28.2 ±.09 leaves to 26.7 it .13 leaves. This is a 
slightly lower point than that of the original Fg distribu- 
tion, but it was calculated from only 76 individuals. A 
conservative estimate of the significance of the results 
would probably be as follows: the mean of the minus 
strain has shifted slightly but permanently and is now 
fixed, while the mean of the plus strain has not changed 
but has shown evidence of some heterozygosis in one gen- 
eration. 

We come finally to consider Families No. 27 and No. 82, 
the data on which are listed in Tables XIV and XV. Two 
generations of both plus and minus . selection were re- 
corded for Family No. 27, but only plus selections of 
Family No. 82 were grown. There is no necessity for 
considering either in detail because a simple inspection of 
the tables shows that selection has accomplished nothing. 

Conclusions 

The cumbersome and no doubt dry details of the ex- 
periments to the close of the year 1912 having been de- 
scribed, let us give a brief resume of the conclusions that 
we believe may reasonably be drawn from the data that 
have been offered. There can be no doubt that the orig- 
inal *'Halladay" type of tobacco, isolated and propa- 



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42 THE AMERICAN NATURALIST [Voi^XLVin 

gated by Mr. Shamel and Mr. Halladay from the cross 
between ^^ Havana" and *' Sumatra" tobaccos, arose 
through the segregation and recombination of the Men- 
delian factorial differences of the two plants, and not as 
a mutation. It is simply a union of the factors that stand 
for leaf size and height of plant in the '^Havana" variety 
with the factors that bring about leaf shape and high 
number of leaves in the ^^ Sumatra" variety. It hap- 
pened that the somatic characters of these varieties ac- 
count for all the characters of the hybrid. At the same 
time one must remember that strains were obtained by 
selection that averaged higher in number of leaves than did 
even the * * Sumatra * * parent. We can only conclude from 
this fact that the difference between the ''Havana" and 
the ''Sumatra" varieties in leaf number is greater fac- 
torially than somatically. Besides certain factors com- 
mon to the two varieties, the factors for leaf number in 
"Havana" tobacco might be represented by the letters 
AA, and those of "Sumatra" tobacco by the letters BB, 
CC, DD, EE. By recombination, this would give plants 
with a smaller number of leaves than the "Havana" 
variety and plants with a greater number of leaves than 
the "Sumatra" variety. Both combinations were ob- 
tained; and further, the theory has been shown to be cor- 
rect by the results of other crosses where both types ap- 
peared (Hayes, *12). It is probably unwise to suggest too 
concrete a factorial analysis of the cross, yet the factorial 
difference assumed above will account for all of the facts 
obtained, by simple recombination. We assume a factor 
in the heterozygous condition to account for the produc- 
tion of one leaf and a factor in the homozygous condition 
to account for the production of two leaves. The mean 
of the " Havana" variety is about 20 leaves and the mean 
of the "Sumatra" variety about 26 leaves. Somatically 
there is a difference of 6 leaves or three factorial pairs 
for which to account. But in order to have the theory 
coincide with the facts there must be at least one (pos- 
sibly two or three) factorial difference that does not show 
in the two varieties. The meaning of this statement can 



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No. 565] CHANGES PRODUCED BY SELECTION 43 

be shown best by an illustration. The 20 leaves of the 
" Havana*' variety and the first 20 leaves of the ** Suma- 
tra '* variety are represented by 10 pairs of factors, of 
which nine are the same and one different in the two 
strains. The ** Havana'* variety is nine leaf factors plus 
A A, the first 20 leaves of the '^Sumatra" variety are nine 
leaf factors (the same as those in the ** Havana") plus 
BB. The additional leaf factors of the ** Sumatra" are 
CC, DD. EE. With these assumptions, the recombina^ 
tions of a tetra-hybrid will represent our facts fairly 
accurately. But, as was stated above, it does not seem 
wise to take this interpretation of the facts too literally. 
That some such factorial combination will represent our 
facts superficially there can be no doubt, but in reality if 
one could grow hundreds of thousands of individuals and 
follow the behavior of each he would likely find himself 
constrained to represent his breeding facts by a much 
more complex system. There would probably be gametic 
couplings and factorial differences whose main effect 
would be on some entirely different character or complex 
of characters, but which would have some slight jurisdic- 
tion over leaf determination. To become diagrammatical, 
the unit characters of a house are its cornices, its win- 
dows, its floors and what not, but a collection of these 
components is not a house. We may even exchange 
dormer windows with our neighbor, but we can exchange 
them only if they fit. Again, we may put on a coat of 
paint, a color unit, but this color unit affects the appear- 
ance of many other parts that are just as truly units. 

The essential part of our conception of the origin of 
this hybrid type is that recombinations of characters 
quantitative in their nature can be expected and predicted 
in crosses in exactly the same manner as is done with 
qualitative characters. On the other hand, it must be 
borne in mind that here was a hybrid type that appeared 
to be breeding true to the general characters that we have 
described, in the F4 generation. That it was not breed- 
ing true is clear from the results of the selection experi- 
ments, yet out of the small number of Fg and Fe families 



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\ 



44 THE AMERICAN NATURALIST [VoL-XLVHI 

taken tinder observation at least two were found to be 
breeding true for all practical purposes in the Fg and F^ 
generations. We were able to reproduce the ^* Havana '^ 
type by continued selection in Family 77 and were able 
to produce strains breeding approximately true to 30 
leaves or so by the selection of mother plants in several 
families. But can we say that any of our families are 
now fixed so that no progress can be made by selection? 
We can not. But we can say that some of them are so 
constant that it would be a loss of time for selection to be 
continued for economic results. It is important to know 
whether plant or animal populations can reach such a 
state of constancy by inbreeding that no profitable results 
can afterwards be obtained by the practical breeder. We 
believe it demonstrated by even these few data that such 
a state, a homozygous condition, occurs in a definite pro- 
portion of Fa offspring, and can be propagated commer- 
cially at once if a suflBcient number of families are grown 
to be relatively certain of including the desired com- 
bination. 

As to the problem of theoretical importance, the ques- 
tion of the true constancy of homozygotes generation 
after generation, we believe it to be fair to conclude that 
a state so constant is reached, that even for the theoret- 
ical purposes of experimental genetics it may be assumed 
as actually constant. Further experiment and larger 
numbers may show that selection can always cause a shift 
in the mean, but will necessarily be a shift so slight that 
it can be detected only by a long-continued experiment 
and enormous numbers. Assuming for the purpose of 
argument that this is the case, the matter would affect 
only the question of the trend of evolution. It may come 
to be believed, from evidence now unknown, that evolu- 
tion may progress slowly in this manner, but if it does, 
its course can hardly be demonstrated experimentally be- 
yond a reasonable doubt. The problems of experimental 
genetics can be attacked, however, from the standpoint 
that experimental evidence of the shifting of the mean of 
a homozygous population by selection is negligible. 



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No. 565] CHANGES PRODUCED BY SELECTION 45 

Mutations may occur. We have shown the origin of 
one family by a very wide mutation. In this particular 
case it was not diflScult to show that a constitutional 
change took place in a single germ cell of the mother 
plant. It was only by a lucky chance that this fact could 
be demonstrated, for with smaller changes such proof 
would be impossible ; but there is no reason to believe that 
this phenomenon is imique or even rare. It is much more 
reasonable to assume that mutations usually arise in 
single gametes than that the same change occurs simul- 
taneously in many germ cells. One should expect the 
somatic result of a mutation in an hermaphroditic plant 
— ^the sporting plant itself — ^not to breed true, therefore, 
but to behave as an Fj hybrid between a mutating and an 
unchanged germ cell. It is true that the mutations ob- 
served by DeVries in (Enothera Lamarckiana are sup- 
posed to have bred true, but this is sometimes question- 
able even from DeVries 's own data. The Lamarckiana 
'* mutants** that did breed true are much more reason- 
ably explained as segregates from complex hybrids. 
They can be interpreted by Mendelism with no essential 
outstanding facts, but if they are to be interpreted as 
mutations, several discrepancies between what actually 
occurred and what should be expected on DeVries 's own 
theory must be explained. It must be shown why the 
changes took place in numerous germ cells, — in both the 
male and the female gametes, — and why these germ cells 
always fused at fertilization ; for the changed germ cells 
must have fused with each other because majiy Lamarck- 
iana plants were produced by the same mother plants that 
produced the mutations, while the mutations are sup- 
posed to have bred true. On the only other possible theory 
of mutation, that the change occurred in the developing 
zygote after fertilization, one would have to explain why 
the mutants did not often appear as bud variations, in- 
stead of these being much rarer than the supposed muta- 
tions, as is actually the case. 

We do not deny the theory of mutation as modified to 



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46 THE AMERICAN NATURALIST [Vol. XL VIII 

assume only that constitutional changes usually occur in 
the germ cells, but on this belief the sporting plants must 
often be F^ hybrids, and the plant breeder must resort to 
selection to isolate his pure mutation. And by the same 
reasoning one gametic change may produce many new 
creations, for there is a chance to recombine it with all the 
known gametic differences in the species. 

No one can say how often mutations arise. It is likely 
that changes other than the one observed took place in 
our tobacco experiments, but it is not likely that they 
are suflBciently numerous to base a system of selection 
within a pure race on the possibility of their occurrence. 
The fact that no changes ensued that could be detected in 
several of our selected lines is an argument against it. 
The comparatively large jumps are the ones likely to 
have the greatest economic importance, and these are 
easily detected without refined methods of procedure. 
Small jumps can be economically important only if they 
are numerous, and, as there are absolutely no data to 
show either that they are numerous or that changes can 
be produced rapidly within homozygous pure lines through 
any other cause, it seems unwise to recommend that the 
practical breeder expend time and money to bring about 
results that either can not be expected at all or that are 
so slow and so trifling that they can not be detected in 
carefully planned and accurately executed genetic inves- 
tigations. On the other hand, the results of the last de- 
cade show that important economic results can be ob- 
tained easily and surely by selection from artificial hy- 
brids or from the natural hybrids that occur in cross- 
fertilized species by the recombination of Mendelian 
factors. We believe, therefore, that the isolation of ho- 
mozygous strains from mixtures that are either mechan- 
ical or physiological, that are either made artificially or 
are found in nature, offers the only method of procedure 
that the practical plant breeder will find financially 
profitable. 

Finally, we should like to call attention again to the 



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No. 565] CHANGES PRODUCED BY SELECTION 47 

practical importance of determining the duration of the 
period in the course of which particular plant characters 
are responsive to the action of environmental influences. 
The character complex that has been the basis of this 
study is a striking illustration of how results from such 
investigations may be applicable to farm practise. One 
may plant a portion of the seed from a self-pollinated 
tobacco plant on poor soil or on good soil and the average 
number of leaves per plant and the general variation of 
the plants in number of leaves will remain nearly the 
same in both cases.* But seed selected from mother 
plants grown on the good soil will produce plants aver- 
aging slightly higher in leaf number than the plants com- 
ing from seed on mother plants whose environment is 
poor. Consequently, it is better to select seed from well- 
developed mother plants — smother plants whose environ- 
ment has been good — ^than from mediocre mother plants. 
There is no question here of the inheritance of an acquired 
character or of continuing to raise the number of leaves 
by cultural treatment. One simply takes advantage of 
the fact that during seed formation there is a period of 
mobility at which time the potential number of leaves of 
the young plant are practically fixed. Pending the end 
of this critical period, the number of leaves can be in- 
fluenced by external conditions within the limit of fluctu- 
ating variability. 

In the same connection, the effect of time of planting 
on the tobacco plant should again be mentioned, as this 
also emanates from environmental change. The actual 
number of leaves is, of course, practically fixed at the 
time of setting the plants in the field, but this is not true 
of the number of leaves that will have a commercial 
value. For example, a seedling with 26 potential leaves 
is planted. If it is planted when about four inches high, 
the general physiological disturbance due to transplanta- 
tion is negligible and the plant continues its normal cycle 
of development without a pause, bringing to maturity 

3 Gamer's (:12) results on Maryland Mammoth are an exception to this 
statement because this variety is indeterminate in growth. 



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48 THE AMERICAN NATURALIST [Vol-XLVTEI 

about 22 leaves. If planting is delayed until the seedling 
is eight or ten inches high, there is a different state of 
affairs. Development is arrested, the plant pauses to ad- 
just itself to the change. It soon recovers and continues 
its normal ontogeny, but the period of reduced growth 
has left an ineffaceable record. Several of the leaves — 
among them the more valuable leaves — ^have been so 
affected during this readjustment, that they develop to 
only a fraction the size that they should attain because 
the intemodes between them are so short, due to the con- 
stricted development that normal metabolism does not 
occur. Thus there is a loss of one or two leaves, which 
on several acres of tobacco may make the difference be- 
tween profit and loss. Hence, the grower should not de- 
lay setting his plants in the field until they have become 
overgrown in the seed bed. 

March, 1913 

LITERATURE CITED 

Davis, B. M. G«netical Studies in CEnothera, III. Amsr. Nat., 46: 377- 

427. 1912. 
East, E. M. Inheritance of Flower Size in Crosses between Niootiana 

Species. Bot, Gae,, 55: 177-188. 1913. 
East, E. M., and Hayes, H. K. Inheritance in Maize. Conn. Agr. Exp. Sta. 

BuU. 167: 1-142. 1911. 
Garner, W. W. Some Observations on Tobacco Breeding. Ann. Rpt. Amer. 

Breed. Assoc., 8: 458-468. 1912. 
Hayes, H. K. Correlation and Inheritance in Nicotiana Tdbacum. Conn. 

Agr. Exp. Sta. BuU. 171: 1-45. 1912. 
Heribert-Nilsson, N. Die Variabilitat der (Enothera LamarcHana und das 

Problem der Mutation. Ztschr. Abstam, u. Vereh,, 8: 89-231. 1912. 
Jennings, H. S. Heredity, Variation and Evolution in Protozoa, I. Jour. 

Exp. Zool., 5: 577-632. 1908. 
. Heredity, Variation and Evolution in Protozoa, II. Proo. Amer, 

Phil. Soc, 47: 393-546. 1908. 

Assertive Mating, Variability and Inheritance of Size, 'in the Con- 



jugation of Paramecvum. Jour, Exp. Zool., 11: 1-133. 1911. 
Johannsen, W. Uber Erblichkeit in Populationen und in reinen Linien. 

Jena, Gustav Fischer, pp. 1-615. 1903. 
Pearl, Raymond. Inheritance of Fecundity in the Domestic Fowl. Ameb. 

Nat., 45: 321-345. 1911. 
Shamel, A. D. New Tobacco Varieties. Yearbook U. S. Dept. Agr., 1906: 

387-404. 1907. 
Tammes, Tine. Das Verhalten fluktuierend variierender Merkmale bei der 

Bastardierung. Bee. Trav. Bot. N^erl., 8: 201-288. 1911. 



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GYNANDEOMOEPHOUS ANTS DESCEIBED DUE- 
ING THE DECADE 1903-1913 

Pbofbssob WILLIAM MORTON WHEELER 
BussiT Institutiok, Habvabd Ukivxbsitt 

In 1903 I described six gynandromorphous ants and 
reviewed the previously recorded cases, seventeen in 
number. Although many thousand ants have since passed 
through my hands, I have failed to find any additional 
cases. Other observers, however, have been more for- 
tunate and have described seven within the past decade. 
As these are all very interesting, it seems advisable to 
give a brief account of them as a sequel to my former 
paper. 

1. Lateral. Gynandbomobph of Cabdiocondyla batesi 

FOBBL. VAB. NIGBA FoBEL. SaNTSCHI (1903, p. 324, 

Fig. 5, i) 

This specimen is female on the right and partly male 
on the left side. The male portions are sharply marked 
off from the black female portions by their testaceous red 
color. The line of demarcation, very clear in front, starts 
at the anterior clypeal border and divides the head into two 
nearly equal parts, but leaves the median ocellus on the 
male side. It then divides the pronotum down the middle 
and the three anterior quarters of themesonotum. Thence 
the line fades out on the right side so that the whole pos- 
terior border of the mesonotum is male. Three quarters 
of the prescutellum and the anterior half of the scutel- 
lum are male. The epinotum and the abdomen are female 
throughout, but the female genitalia are slightly asym- 
metrical on the left side. The fore and middle legs on 
this side and a portion of the mesosternum are male. 
There are wings on both sides, but the anterior one on the 
female side was lost after capture. Those on the left 

49 



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50 THE AMERICAN NATURALIST [VoL.XLVin 

side are well-developed, with distinct venation and pale 
pterostigma, and are inserted in a distinctly male area. 
The specimen was not dissected. 

Santschi found this ant in a nest with females at Kai- 
rouan, Tunis, but without males, either of the winged or 
of the ergatomorphic type, which is peculiar to this and 
some of the other species of Cardiocondyla. His atten- 
tion was attracted by the bizarre movements of the speci- 
men, as it turned around rather quickly in circles about 
10 cm. in diameter, with the male portion inside. In 
other words, owing either to the asymmetry of its brain 
and visual organs or to differences in the length of the 
legs on the two sides of the body, it made circus move- 
ments like a normal insect which has had one of its eyes 
or optic ganglia injured. 

2. Lateral Gynandromorph of Anergates atratulus 
ScHENCK. — ^Adlbrz (1908, p. 3, Fig. 1, a, h, c, d and /) 

An imperfect lateral gynandromorph, with the head 
largely male on the left, female on the right side, the light 
color of the male being sharply marked off from the dark 
color of the female only anteriorly. Thorax in front 
female, with wings equally developed on both sides (the 
male Anergates is wingless and pupoid!), but with pale 
(male) coloration on the left and dark (female) colora- 
tion on the right side, the line of division between the 
two neither sharp nor straight and the whole postscutel- 
lum blackish brown. Abdomen with irregular arrange- 
ment of color. Petiole black on the right, grayish yellow 
on the left ; postpetiole mostly blackish brown, but with 
a large grayish yellow spot on the left side of its anterior 
surface. Third dorsal tergite blackish brown on the right, 
grayish yellow on the left side. Remainder of gaster 
grayish yellow, tinged here and there with pale brown. 
Third tergite with a median longitudinal groove which 
runs back on to the succeeding segment as in the virgin 
female. The left side of the abdomen has seven com- 
plete segments and well-developed genitalia; the right 



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No. 565] QTNANDBOMOEPHOUS ANTS 51 

side has only six complete segments and a membranous, 
incomplete seventh^ The genitalia on the right side are 
imperfect, the volsella being represented only by a piece 
corresponding to its dorsal portion and the stipes is com- 
pletely lacking. The legs are of the female type, except 
the left fore leg, which is male, although the tibial spur 
(strigil) is pectinate as in the female. This spur is known 
to be nonpectinate in male Swedish, but pectinate in male 
Swiss Anergates specimens. 

On dissecting this specimen, which he took from a large 
Anergaies-Tetramorium colony near Arkosund in Oster- 
gotland, Sweden, Adlerz found on the left side a well- 
developed vesicula seminalis, receiving a vas deferens 
half as long. No traces of female reproductive organs 
nor of the poison gland and vesicle could be detected. 

Of particular interest was the behavior of this gynan- 
dromorph, because, as Adlerz says, it evidently felt itself 
to be a male but was treated by the normal males in the 
colony as a female. Its movements were somewhat live- 
lier than those of normal males, and it at first made feeble 
attempts to copulate with the females and was treated 
with indifference by the males. A few days later it be- 
came more energetic and persistently attempted to copu- 
late, especially with one particular female, although 
always unsuccessfully while it was under observation. 
It was evidently inflamed with the insatiable sexual appe- 
tite so characteristic of the normal Anergates males, 
which, being wingless, always mate with their sisters be- 
fore they fly out of the parental nest. On the following 
day, however, a normal male made the most persistent 
efforts for several hours to mate with, this same gynan- 
dromorphous individual. Adlerz concludes that 

this indicates that the males regarded it as a female. Of course, we 
may suppose that its wings made it seem like a female and attracted the 
male, but from the fact that males attempt to mate even with female 
pupae and therefore with a stage which has not yet developed wings, it 
is more probable that the male was attracted to the gynandromorph by 
some female odor. At any rate the double nature of the gynandromorph 



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62 THE AMEBIC AN NATURALIST [VoL-XLVHI 

is even more strongly indicated by the facts just recorded than by its 
morphol6gical peculiarities. 

3. Latbbal Gynandbomorph of Anbrgates atbatulus 
ScHENCK. — Adlebz (1908, p. 5, Fig. 2, a, 6, c, d and e) 

An imperfect lateral gynandromorph, male on the left, 
female on the right side, resembling the preceding speci- 
men, but with the dark female color more pronotmced on 
the male side of the head There were well-developed 
wings on both sides of the thorax, which was of the female 
form though dark on the right and pale on the left side, 
except the epinotum, which was grayish yellow through- 
out. Abdomen in color and form almost typically male, 
with the genitalia well-developed on both sides, but with 
a feeble mid-dorsal impression recalling the condition in 
the virgin female. Legs of the female type, except the 
left fore one, which is somewhat shorter and thicker as in 
the male and with the tibial spur (strigil) cleft but not 
pectinated. 

Dissection showed the reproductive organs to be in the 
same condition as in the preceding specimen; i. e,, they 
were present only on the left side and consisted of a 
rather large vesicula seminalis with its vas deferens. No 
traces of female reproductive organs, nor of a sting or 
poison apparatus were to be found. 

This specimen was taken from the same nest as the 
preceding. 

4. Lateral Gynandromorph (Ergatandromorph) of 
Formica sanguinea Latreille. — Donisthorpe (1909, 

p. 464, Fig. 1) 

A nearly complete lateral ergatandromorph, with the 
right antenna, mandible and eye, and right and median 
ocellus male and the left antenna, mandible, eye and ocel- 
lus of the worker type. Head black, except the left 
mandible, left half of clypeus, left cheek and a small patch 
in front of the eye, which are red. Thorax and petiole 



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No.6e6] GTNANDB0M0BPH0U8 ANTS 58 

male on the right, worker on the left, the line of division 
running to the left of the median line so that the black of 
the right side of the mesonotnm encroaches on the red 
color of the left side. Petiole and gaster sharply divided 
into black right and red left halves, the right half of the 
latter also with male pilosity and sculpture. External 
male genitalia and anal stemite on the right side. The 
red and black coloration is sharply divided on the venter, 
but the C0X8B are all black and red as on the male, and the 
legs on both sides are somewhat infuscated. Tarsi longer 
on the right (male) side. Wings well developed, on the 
right side only, with pale veins and stigma and more like 
those of the female. Length 7 mm. 

This specimen was taken by Mr. Donisthrope July 20 
or 21 from a large colony in Bewdley Forest, England. 

5. Latebal Gtnakdbomobph of Fobmica sakouinba 
Latbeille. — DoKiSTHOBPB (1909, p. 464, Fig. 2) 

A nearly complete lateral gynandromorph, male on the 
left, female on the right side. The head is of the female 
type, rather small, with both of the antennae and the ocelli 
female and the left eye a little larger than the right. 
Head black, clypeus and right mandible red ; thorax evenly 
divided into a black left and red right half, but only the 
upper right comer of the epinotum red. A piece of the 
scutellum and postscutellum red on the left side where 
the wing is inserted. Petiole sharply divided into a red 
right and left black half. Gaster black, the pilosity and 
sculpture on the right half female, on the left half male, 
the color being sharply defined on the venter. Legs and 
coxaB female on the right, male on the left side. External 
genitalia of the male type present on the left side. Both 
pairs of wings fully developed, but the stigma and veins 
darker as in the male. Length 9 mm. 

This specimen was taken from the same colony as the 
preceding. 



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64 THE AMERICAN NATURALIST [VoL.XLVin 

6. Fbontal Gynandbomobph of Solbnopsis fugax 
Latreillb. — Santschi (1910, p. 649) 

The head and thorax in this specimen are female, the 
pedicel and gaster male. The head is somewhat smaller 
than in normal females. The copulatory organs are those 
of the normal male. Santschi remarks that it ** would be 
interesting to observe the sexual behavior of such an indi- 
vidual possessing a female brain and male genitalia.*' 

7. Lateral Gynandbomobph (Ebgatandbomobph) of 

MyBMICA SCABBINODIS NyLANDBB. — DONISTHOBPE 

(1913, p. 44, PL I) 

A nearly complete lateral ergatandromorph ; worker on 
the right, male on the left side, the former being blackish, 
the latter reddish yellow. Eight half of head larger than 
the left, but with a smaller eye, striatorugose; right an- 
tenna yellow, with a three- jointed club, its scape with the 
usual strong lateral tooth at the basal flexure. Bight 
half of thorax yellow, its epinotal half with a strong spine ; 
right half of petiole and postpetiole yellow, rugose and 
punctured ; right half of gaster pale fuscous yellow. Legs 
on the right side of the worker type, yellow. Left side of 
head blackish, ptmctate, not striatorugose, with a larger 
eye and the median and left ocellus ; its antenna fuscous, 
with four-jointed club. Left half of thorax blackish, its 
epinotal portion unarmed ; left half of petiole and post- 
petiole smooth, fuscous black. The greater part of the 
left half of the gaster had been eaten away but the re- 
mainder was darker fuscous th€in the right. Legs on left 
side of the male type, fuscous ; wings on the left side only. 

Donisthorpe remarks that this specimen, which was 
picked up dead by Mr. Dollman at Ditchling, England, ap- 
proaches the var. sabuleti Meinert in having the left 
ant ennal scape longer than in the typical male scabrinodis 
and the tooth on the right antenna large. 

In conclusion I would call attention to a peculiar ant 
described by Mayr (1868, p. 60) from the Baltic amber 



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No. 565] GTNANDBOMOBPHOUS ANTS 55 

and designated as a *'Zwitter** (gynandromorph) of 
Hypoclinea constricta Mayr, or Iridomyrmex constrictits 
as we must now call the species. Through the kindness 
of Prof. A. Tornquist, of the University of Konigsberg, 
I have been able to examine this specimen in connection 
with many other amber FormicidsB. The general struc- 
ture of the head, thorax and gaster is that of a worker, 
though the thorax is not typical, as the base of the epino- 
tum is less convex and less abruptly elevated, so that the 
angle between it and the declivity is less pronounced in 
profile. Mayr does not mention that the eyes are decid- 
edly larger and more convex than in the normal worker 
and therefore more like those of the male. There are a 
few small white spots or bubbles on the vertex, which re- 
semble small ocelli, but these organs seem to be actually 
absent. The antennsB are 13-jointed and very long, as in 
the male ; the scapes, however, are like those of the worker, 
but extend well beyond the posterior borders of the head, 
whereas joints 2-11 of the funiculi are cylindrical, sub- 
equal and fully three times as long as broad, the terminal 
joint being somewhat longer than these, the first shorter. 
In the gaster, whioh is shaped as in the normal worker, 
there are five distinctly visible segments, but the tip shows 
•clearly the small, hairy, external genital valves (stipes) 
of the male. The legs are also more slender than in the 
normal worker and therefore more like those of the male. 
At first sight thissingular insect seems to be a gynandro- 
morph, as Mayr supposed, or more specifically, an erga- 
tandromorph of the blended type, with worker characters 
preponderating in the trunk and those of the male pre- 
ponderating in the eyes, appendages and genitalia. It is 
possible, however, to regard this specimen as an ergato- 
morphic male, like those which occur normally in certain 
species of Ponera, Cardiocondyla, Formicoxenus, Sym- 
myrmica and Technomyrmex. Unfortunately we are not 
in a position to decide between these alternatives, because 
we are dealing with a single fossil specimen and are not 
even sure that it belongs to the species to which Mayr 



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56 THE AMERICAN NATURALIST [VoL.XLVni 

assigned it. Still the case is interesting if only because 
it suggests the further question as to whether the ergato- 
morphic males in the genera above cited may be regarded 
as originally frontal ergatandromorphs, with worker 
head and thorax and male gaster, that have become the 
only males of the species. If this is true, the ergato- 
morphic males may have arisen by mutation from patho- 
logical or teratological forms and have been preserved in 
certain species in which peculiarities of habit rendered the 
fecundation of the virgin females in the nest by wingless 
males more advantageous than the type of mating ex- 
hibited by the nuptial flight. A moment *s reflection shows 
that the nuptial flight is a highly advantageous institu- 
tion in common ants that form large colonies, but must be 
as decidedly disadvantageous in the case of very small, 
rare ants whose colonies are very sporadic and comprise 
only a few individuals. This is actually the condition 
seen in all the species with ergatomorphic males in the 
genera Ponera, Cardiocondyla, Formicoxenus, Symmyr- 
mica and Technomyrmex, and may be supposed, there- 
fore, to accotmt for the substitution of the wingless, erga- 
tomorphic for the normal winged males in these species. 

LITERATURE 

1908. Adlerzi G. Zwei Gynandroinorpheii von Anergates atratulus Schenck. 

Arhiv. for ZooL, V, 1908, No. 2, 6 pp., 2 pis. 

1909. Donisthorpe, H. S. J. K. Formica sanguinea, Ltr., at Bewdley, with 

an Account of a Slave-raid, and Description of two Gynandro- 

morphs, etc. Zoologist, 1909, pp. 463-466, 2 figs. 
1913. Donisthorpe, H. S. J. K. Some Notes on tihe Genus Myrmica, Ent. 

Becord, XXV, 1913, pp. 1-8, 42-51, 1 pi., 10 text figs. 
1868. Mayr, G. Die Ameisen des batischen Bernsteins. Beiir, Naturk, 

Preussens, 1. Konigsberg, 1868, pp. iv + 102, 5 pis. 
1907. Santschi, F. Fourmis de Tunisie Captur^es en 1906. Bev. Suisse 

Zool, XV, 2, 1907, pp. 305-334, 7 figs. 

1910. Santschi, F. CJontributions k la Faune Entomologique de la 

Roumanie. Formicides Captur^es par Mr. A. L. Montandon. 
Bull, 8oc. 8ci. Bucharest, XIX, No. 4, 1910, pp. 648-651. 
1903. Wheeler, W. M. Some New Gynandromorphous Ants, with a Review 
of the Previously Recorded Cases. Bull, Amer, Mus, Nat, Hist^ 
XIX, 1903, pp. 653-683, 11 figs. 



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SHORTER ARTICLES AND DISCUSSION 

ON THE RESULTS OP INBREEDING A MENDELIAN 

POPULATION: A CORRECTION AND EXTENSION 

OP PREVIOUS CONCLUSIONS* 

In a recent paper by the present writer on inbreeding,* the con- 
clusion was reached {loc, cit., p. 608) 

that no increase in the proportion of homozygotes in the population 
follows inbreeding save under one or the other of two special condi- 
tionsy viz.: 

(a) Continued self-fertilization. 

(b) Some form of gametic assortative mating which increases the 
natural probability of like gametes uniting to form zygotes. 

This conclusion is entirely correct as it stands, but also barren, 
for it overlooks the very essential fact that any sort of inbreed- 
ing involves in greater or less degree ''gametic assortative mat- 
ing." The mathematical demonstration on page 608 of the paper 
referred to is also entirely correct so far as it goes, but it stops 
too soon. Up to the third generation of brother X sister mating 
starting from a population of complete heterozygotes there is no 
increase in the proportion of homozygotes beyond that prevailing 
in a general Mendelian population. In the fourth and later gen- 
erations there is, however. The blunder, kindly pointed out to 
me by Professor E. M. East, which in retrospect seems altogether 
too stupid even to be possible, was in the failure to recognize that 
after the second generation the constitution of the family would 
no longer be the same as that of the population. This is the point 
which makes illegitimate the extension by induction of the results 
up to the third generation to the generations beyond. 

The genei|l conclusion of the former paper quoted above, 
should then l^as follows : An increase in the proportion of homo- 
zygotes in the population will follow inbreeding of any sort, 
though at different rates for different types of inbreeding, 
because any inbreeding involves homogamy (or assortative fnat- 
ing) in some degree. 

Having made clear the location and nature of the error I desire 
now to show in some detail exactly what results follow from con- 

1 Papers from the Biologieal Laboratory of the Maine Agricultural Ex- 
periment Station^ No. 54. 

1 < < A Contribution Towards an Analysis of the Problem of Inbreeding, * ' 
Ambucan Naturalist, Vol. XLVn, pp. 577-614, 1913. 

67 



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58 THE AMEBIC AN NATURALIST [VoL-XLVHI 

tinued brother X sister mating in a Mendelian population. To 
this we may now proceed. 

The Distribution op a Mendeuan Population in Succbssivb 

Generations with Continued Brother X Sister 

Mating 

Let us start with a population composed entirely of complete 
heterozygotes. We shall consider a single character pair, A 
denoting the dominant character, and a the recessive. The com- 
plete heterozygote individual will then be Aa, and will produce 
in equal numbers A and a gametes. 

In making an analysis of the effect of inbreeding on the popu- 
lation it will be necessary to deal not merely with the distribu- 
tion of individuals in each generation, but also with the distribu- 
tion of families of the several types. Each mating will produce 
an array of families, as well as an array of individuals. The 
standard family throughout this discussion is taken as including 
32 individuals, of which 16 are males and 16 females. It is 
further assumed that there is no sex-linkage of characters, and 
that in any family there will be an equal number of brothers and 
sisters of each zygotic constitution represented. One family of 
16 pairs of brothers and sisters will make 16 matings and pro- 
duce 16 families of 32 individuals each. This constant rate of 
fertility is assumed throughout the discussion. 

Every mating made is of a brother with his sister. 

With so much by way of preliminary definition of the limita- 
tions of this investigation, let us proceed to the actual analysis. 

First Oeneration 

Constitution of the Population. — ^By hyi)othesis all individuals 
are Aa. 

Proportion of Homozygotes in this Oeneration. — per cent, 
of the whole population. 

Matings to Produce the Second Oeneration. — Start with one 
brother X sister pair of individuals from this population. The 
mating will be Aa X Aa. This will produce one family, 8AA 
+ 8Aa + 8aA + 8aa. 

Second Generation 

Constitution of the Population. — 8-4.-4. + SAa -f- 8-4.a -f- 8aa. 
Proportion of Homozygotes in this Oeneration. — 50 per cent, 
of the whole population. 



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No. 565] 8H0BTEB ARTICLES AND DISCUSSION 



59 



Matings io Produce the Third Oeneration. — ^The matmgs of 
the one family of this generation will be as follows: 



cfo" 


99 


d'd' 


99 


(1) AA 


(1) AA 


(9) oA 


(3) oA 


(2) AA 


(5) AA 


(10) o4 


(7) oA 


(3) AA 


(9) AA 


(11) aA 


(11) a4 


(4) AA 


(13) AA 


(12) oA 


(15) oA 


(5) Aa 


(2) .ia 


(13) aa 


(4) «a 


(6) Aa 


(6) Aa 


(14) ao 


(8) aa 


(7) Aa 


(10) 4a 


(15) aa 


(12) aa 


(8) Aa 


(14) 4a 


(16) aa 


(16) oa 



TfctVd Oeneration Families Produced. — (Note: the numbers 
in parenthesis are to identify matings and their consequent 
families.) 





AA 


Aa 


aA 


ma 


(1) 


33 
16 
16 








(2) 


16 
16 
32 






(3) 






(4) 






(5) 


Vft 

8 
8 


16 
8 
8 




(«) 
(7) 
(8) 


8 

8 

16 


8 

8 

16 


(9) 


16 

8 
8 


16 
8 
8 




(10) 
(11) 
(12) 


8 

8 

16 


8 

8 

16 


(13) 




32 
16 
16 




(14) 






16 


(15) 






16 


(16) 






82 











Third Oeneration 
Constitution of the Population. — 

128AA + 1284a + 12804 + 128aa. 

Proportion of Homozygotes in this Oeneration. — 50 per cent, 
of the whole population. 

Fourth Oeneration Families Produced. — The third generation 
families, when mated, will produce families as follows: 

Summarized this gives the following fourth generation families 
produced : 

(1)4 86 families like (1), 
(2)4 24 families like (2), 



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60 



THE AMERICAN NATURALIST [Vol. XLVIH 



(3)4 4 famiUes 
(4)4 24 families 
(5)4 80 families 
(6)4 24 families 
(7)4 4 families 
(8)4 24 families 
(9)4 36 families 



like (4), 
like (5), 
like (6), 
like (8), 
like (13), 
like (14), 
like (16), 





AA 


Aa ' Aa 


aa 


Family (l)t will produce . . 16 families of constitution 


32 
32 
16 
16 

8 
8 








Families (2)t will produce 4 families of constitution 








(3)i, (5)i will produce. . . . +4 families of constitution 


16 

"s" 

8 






and (9)i will produce +4 families of constitution 

each will produce +4 families of constitution 

and (13)i 


16 

8 
8 


"s" 

8 


each 








Families (6)i will produce . 1 family of constitution 


32 
16 

"ie * 

8 


1 1 


(7)i, (10)t will produce. . . +2 families of constitution 


16 






and (ll)l will produce t , - +1 family of constitutinn 


32 

***8 " 
16 






+2 families of constitution 
+4 families of constitution 
+2 families of constitution 
+1 family of constitution 


16 
8 

**32 * 
16 


"s" 

16 


+2 families of constitution 






16 


+1 family of constitution 






32 


Families (8)1 will produce 4 families of constitution 
(12)i, (14)i will produce. . +4 families of constitution 
and (15)t will produce. . . +4 families of constitution 
each will produce -{'4 families of constitution 


8 


8 
16 


8 
'16 ' 


8 
16 
16 






32 


Fftmily (lft)t Will produce 16 fftmiliAif of constitution 








32 













Fourth Oeneraiion 
Constitution of the Population. — 

2560 AA + 1536Aa + 1536aA + 2560aa. 

Proportion of Hotnozygotes in this Generation. — 62.5 per cent, 
of the whole population. 

Fifth Generation Families Produced. — The third generation 
families, when mated, will produce families as follows : 



(1). 


will produce 36 X 16 = 


576 families like 


(1). 


(2). 


will prodDce 24 X 4 = 


96 families like 


(1). 




+ 96 


families like 


(2). 




+ 96 


families like 


(5). 




+ 96 


families like 


(6). 


(3). 


will produce 4 X 16 = 


64 families like 


(6). 


(4), 


wiU produce 24 X 4 = 


96 famiUes like 


(1). 




+ 96 


families like 


(2). 




+ 96 


families like 


(5). 




+ 96 


families like 


(6). 



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Ko.665] 8H0BTER ARTICLES AND DISCUSSION 61 

(5)4 will produee 80 families like (l)t 

+ 80 X 2 = 160 familiee like (2). 

+ 80 families like (4), 

+ 160 families like (5). 

+ 80 X 4 = 320 families like (6), 

+ 160 families like (8). 

+ 80 famines like (13), 

+ 160 families like (14), 

+ 80 families like (16), 

(6)4 will produce 24 X 4 = 96 families like (6), 

+ 96 families like (8), 

+ 96 familiee like (14), 

+ 96 families like (16), 

(7)4 will produce 4 X 16 = 64 families like (6), 

(8)4 will produce 24 X 4= 96 families like (6), 

+ 96 families like (8), 

+ 96 families like (14), 

+ 96 families like (16), 

(9)4 will produce 36 X 16 = 576 families like (16), 

Summarized this gives the following fifth generation families 
produced : 

(1), 848 families like (1), 
(2), 352 families like (2), 
(3), 80 families like (4), 
(4), 352 families like (5), 
(5), 832 families like (6), 
(6), 352 famUies like (8), 
(7), 80 families like (13), 
(8), 352 families like (14), 
(9), 848 families like (16), 

4096 (=16X256). 

Fifth Oeneration 

Constitution of the Population, — 

44,73644 + 20,4804a + 20,48004 + 44,736aa. 
Proportion of Homozygotes in This Oeneration. — 68.75 per 
cent, of the whole population. 
Sixth generation families produced: 

17,216 families like (1), 

4,480 famiUes like (2), 

832 families like (4), 

4,480 families like (5), 

11,520 families like (6), 

4,480 families like (8), 

832 families like (13), 

4,480 famities like (14), 



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62 



THE AMERICAN NATURALIST [VoL.XLVin 
17,216 families like (16), 



65,636 (=16X4,096). 

Sixth Oeneration 
Constitution of the Population, — 

786,43244 + 262,1444a + 262,144a4 + 786,432aa. 



Proportion of Homozygotes in This Oeneration. — ^75 per cent, 
of the whole population. 

From this point on it will not be necessary to carry out the 
work in detail. The final results are given in Table I for four 
more generations. 

TABLE I 

Showing the Constitution of the Population After 7 to 10 
Generations of Brother x Sister Mating 



Gener- 
fttion 


AA 


Aa 


aA 


<Ul 


Percentage 
of Homozj- 

gotesin 
Whole Pop- 
ulation 


7 

8 

9 

10 


13,369,344 

224.395,264 

3.724,541,952 

61,337.501,696 


3,407,872 

44,040,192 

570,425,344 

7,381,975.040 


3,407,872 

44.040,192 

570,425,344 

7,381,975.040 


13,369,344 

224,395,264 

3.724,541,952 

61,337.601,696 


79.69 
83.59 
86.72 
89.26 



It is evident that the proportion of homozygotes is approaching 
100 per cent, in the same manner as in the case of self-fertiliza- 
tion, worked out by East, Jennings and others, but at a slower 
rate. 

In a later paper I hope to take up the problem of the general 
formulae for finding the constitution of a Mendelian population 
after n generations of inbreeding of the different types, and at 
the same time discuss the relation of these results to the coeffi- 
cients of inbreeding described in my former paper. It should be 
specifically mentioned that, in the light of the data here set forth, 
those criticisms of the conclusions of East and Hayes made in my 
former paper^ which were based on the erroneous assumption of 
a fundamental difference between self-fertilization and all other 
forms of inbreeding in respect to homozygosis, have no validity 
whatever. It scarcely needs to be said that the blunder on the 
theoretical side here corrected in no wise affects thS usefulness of 
inbreeding coefficients. Raymond Peabl 

« Cf. Pearl, loc. cit., p. 606, 609 and 610. 



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ISOLATION AND SELECTION ALLIED IN PRINCIPLE 

There are those who folly recognize the influence of natural 
selection in transforming the hereditary characters of a species, 
but are unable to see how isolation should have any effect of that 
kind. They say that you may divide a species into two branches 
between which all possibility of crossing is completely prevented, 
but if the environment surrounding each branch is the same, the 
natural selection to which each is subjected will be the same, and 
no divei^nce of character will take place. They forget that the 
separate branches, if prevented from crossing for many genera- 
tions, are sure to develop different types of variation, and in due 
time different methods of using the same environment, and are 
therefore liable to subject themselves to different foims of selec- 
tion. Again they forget that when the power of dispersal is 
highly developed in a species it may be exposed to diverse en- 
vironments and therefore to diversity of selecting influences, and 
still remain one harmonious species, because free crossing is 
maintained between all parts of the species. As long as there is 
no isolation of different branches, that is, while free crossing con- 
tinues, there is no permanent divergence resulting in diverse 
races or species, even though the one species is exposed to differ- 
ent forms of selection in different parts of its habitat. 

Diversity of evolution, producing many divergent forms of 
animals, could never have arisen without continuous isolation be- 
tween the different forms. 

Again there are those who maintain that selection unaided by 
isolation can not produce transformation. It is true that diver- 
gent groups can not be produced and intensified without isola- 
tion; but a given race may be transformed by selection without 
being divided into two groups by isolation. 

Heredity with variation is the active cause of transformation ; 
isolation and selection are the conditions that shape the f6rms of 
heredity and variation. 

It is a law of heredity, that, if those of a given stock that are 
most alike in hereditary characters mate with each other, there 
will be a tendency in their offspring to a stronger emphasis of 
that character. 

63 



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64 THE AMERICAN NATURALIST [Vol.XLVHI 

Another law of heredity is that as long as free crossing is main- 
tained between the different forms of a species these forms can 
not become widely divergent. The elephant and the mouse could 
never have been developed from one original stock while free 
crossing continued. 

Now there are many ways by which the free crossing of one 
variation with others of the same species may be prevented, but 
they all come under two groups. 

Under selection are classed all the influences enabling certain 
variations to reproduce more successfully than other variations, 
and 80 preventing free crossing between the successful and the 
unsucessful. Under isolation are classed all the influences that 
prevent living, and sexually reproducing creatures, from freely 
crossing. 

Under normal conditions there is no crossing between the ass 
and the horse, though there is reason to believe that the early 
ancestors of each were of one stock freely interbreeding and pro- 
ducing fertile offspring. If isolation had not existed for ages be- 
tween them, they could not have become the separate creatures 
that they now are. Heredity can combine only compatible char- 
acters. In some cases, incompatible characters arise between 
creatures of the same race preventing any crossing between them, 
as when a dextrally twisted moUusk produces a sinistrally twisted 
one; but, in most cases, such incompatibility arises only after 
isolation, through geographical separation, for many generations. 

In view of these facts, is it not plain, that, in the case of a 
variable and plastic organism, races more or less divergent will 
be produced, if for many generations the organism is divided 
into branches that are prevented from crossing! Is not such a 
result just as sure as the gradual transformation of the race 
under a slow change of climate, when the successful variations 
are prevented from crossing with the unsuccessful variations! 

John T. Guuck 

Honolulu, T. H. 



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• > ^ 1 ^ • ... . 

CONTENTS or THE JULY NUMBER . ^ 
Doetrlnts held ai VitaUna. ProfeMor H. & Jen^ngs. 
Tht PrMenoe of the Barred Plumage Pattern in the 

White Leghorn Breed of Fowli. Dr. Philip B. 

Hadley. ' ' 
Shorter Artiolet and Diseuislon: The Geologic Work 

of Termite* in the Belgian Congo. Donald BteeL 
Noteiand LlteraChre^ Work in Geneiicl>roblemiin 

Protozoa at Yale. Profeasor^A. R. Hiddleton. 

Notes on lohthyology. President DaTid Starr 

Jordan. 


OONTENTB OF THe' AUGUST NUMBER 

Oeneti(*al Studies on Oenothera. IV. Dr. Bradley 

Hoore Davis. • 
The Inflnenoe of Protracted and Intermittent Pasting 

upbnQrowth. Dr Sergiuf Morgnlis. 
Cambrian Holothurians. Austin H. Clark. 
Shorter Abides and Discustlon: Viability and CouiT 

ling in Drosophila. P. W. Whiting. TheResnltt 

Obtaiu< d by crossing sea mail L. and Enchlaenfc 

mezicana Schrmd, Mary Q. Lacy. , 


OONTINT8 OF THE •EPTEMBER NUMBER 
Thft Natoral History of «h« Nine-banded Armadmo 
ofTexM. Professor H.H. Newman. 

Genatical Studies on Otnothera. IV. Dr. Bradley 
M. DaTis. 

NotMon a Dlflerential Mortality obserrwl betw««ii 
TWMtmohsonrUandT.moUtor. Dr. Boss Aiken 

OOftDtf. 


CONTENTS OF THE OCTOBER NUMBER 

A Contribution towards an Analysis of the Problem 
of Inbreeding. Dr. Raymond Pearl. 

The Inheritance of Coat Color in Hones. Professor 
W. S. Anderson. 

The Variations in the Numberof Vertebrae and Ven- 
tral Scutes in Two Snakes of the Qenus Reglna. 
Professor Alexander G. Ruthren and Crystal 

Shorter Articles and Reports : The Simultaneous 

fessor R. A. JSmerson. The Fourth International 
Genetic Conference : Dr. Frank M. Surfaee. 


OONTENTB OF THE NOVEMBER NUMBER 

The Bffleet on tho OfTspring of IntozlcAting the Male 
PMwit and tht Transmission of the Dsfttets to 

Shortor Articles Mid Discnssion: Reciprocal Crosses 
between Reeye's Pheesant and the Common 
Rlngneek Pheesant prodncing Unlike Hybrids. 
JohnCPhilUps. 


CONTENTS OF THE DECEMBER NUMBER 

The Fixation of Character in Organisms. By Edward 
Sinnott. 

Ramaley. 
Supplementary Studies on the Differential Mortality 

with Respect to Seed Weight in the Gemination 

ef Garden Beans, n. Dr. J. Arthur Harris, 
Shorter Articles and Discussion : A Croas iUTolTlag 

FourPainofHendelianCaiaractersinMioe. C 

C. Little. J. C.PhiUips. 
Index to Volume XLVH. 


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VOL. ZL7m, HO. 666 FEBKVABT, 1914 



THE 

AMERICAN 
NATURALIST 



A MOHTHLT JOUBSAL 

Seroted to the Advancement of the Biological Scieneea wtOk 

Special Beference to the Factors of Evolution 

COHTEHTS 

Page 
L Some Hew Varieties of Rats and Onlnea-plgs and their Relations to Prob- 
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ZI. ** Dominant" and'* RecesBlye" Bpottlnf In lUoe. C. C. Little - - T4 
m. On DUforentlal Mortality with respect to Seed Weight occurring In Fl«ld 

Onltnres of Plsnm sativum. Dr. J. Artuub Hakbis - . - - 83 
rv. Tne Inheritance of a Recurring Somatic Variation In Variegated Ears of 

MaUe. Professor R. A. Embrson --------87 

T. Restoration of Bdaphosaurus crudger Cope. Professor E. C. Case - - 117 
VI. Shorter Articles and Discussion : 

Humidiiy~ft Neglected Factor in EnyiroDmental Work. Dr. Frank E. Lutz 122 



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66 THE AMERICAN NATURALIST [Vol. XLVm 

race and as a mutation or unit-character variation, retro- 
gressive in nature (i. e., due to loss of some normal con- 
stituent from the germplasm). Each is a simple Mende- 
lian recessive character in crosses with wild race, and 
with certain at least of the tame varieties. The two varia- 
tions have not as yet been combined by intercrossing, but 
this will be attempted soon and, I doubt not, with entire 
success. 

My first information about the new variations was 
obtained from Fur cmd Feather, the oflScial organ of the 
English fanciers, in which appeared advertisements of 
*Hhe new variety*' of black-eyed yellow rat. Now as 
long ago as 1903 Bateson had commented on the singular 
absence of a ** yellow'* variety among rats, noteworthy 
because nearly all mammals kept in captivity have such 
varieties ; and I have since been bold enough to publish 
some speculations as to why this variation had not made 
its appearance. Consequently I was mudh excited to 
learn that it actually had appeared. Miss M. Douglas, 
one of the editors of Fur and Feather, and secretary of 
the National Mouse and Eat Club (of England) very 
kindly answered my inquiries about the new varieties and 
put me in communication with the ** originators,'* who 
have given so clear and full accounts of their procedure 
in establishing the new varieties that even the genetic be- 
havior of the variations is fairly certain, though I pur- 
pose to confirm this fully with experiments which are 
already in progress. 

The pink-eyed variation made its appearance first, so 
far as known, about 1910 or 1911, but it had probably 
been in existence for some time and become rather widely 
diflFused throughout the central part of England, for at 
about the same time pink-eyed wild rats were caught at 
or near Preston and at Chesterfield, cities some 65 miles 
apart. I am informed that Mr. T. Eobinson at Preston 
and Mr. W. E. Marriott at Chesterfield independently 
established the ** pink-eyed fawn" variety, or what would 
better be called the pink-eyed agouti variety, since appar- 



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No. 566] NEW VARIETIES OF EATS AND GUINEA P1Q8 67 

ently it differs from the wild gray (or agouti) variety by 
the pink-eyed variation alone. It is not a true yellow 
variety at all genetically, though (like the pink-eyed gray 
mouse) it resembles one superficially because of the yel- 
low ticking of the agouti fur. 

It is also quite distinct genetically from the albino 
variation seen in white rats, yet its * * dirty white' ' color is 
enough like the appearance of the albino to permit mis- 
taking one for the other. Possibly this is why the pink- 
eyed variation may have been for some time overlooked. 

Mr. Robinson has not answered my inquiries, but Mr. 
Mariott writes in detail about his observations and ex- 
periments. 

Under date of October 11, 1913, he says : 

The first rat with any semblance of fawn in it that I had was canght 
in a trap on a provision merchant's premises in Chesterfield. Yon conld 
searcely call it a fawn, bnt more of a cream or dirty white. I have also 
had fonr others similar to this one, 2 caught at the same place and 2 
caught at a malt-house in close proximity to the other premises, [in aU] 
3 bucks and 2 does, but the only one that I was able to get to breed was 
the first brought to me, which was a buck. When first caught it was 
very wild, in fact it appeared to me to be more wild than an ordinary 
wild rat. It was a source of trouble getting it to mate, killing no less 
than 20 does before mating. I eventually got it mated to 2 does, one a 
pure white for at least 10 generations, and one black-and-white hooded- 
and-striped, or Japanese rat. The result of the pure white cross was 2 
young, a buck and a doe, wMch were agoutis with no white at all,^ The 
result from the Japanese cross was 7 young, 5 does and 2 bucks, which 
were the color of Irish agoutis being agouti color with a white stripe 
running underneath. These results naturaUy caused me great disap- 
I>ointment as I was expecting a fawn colored young one. When the 
young were old enough I mated father and daughter, result nil; mother 
and son, result ntl; brother and sister. The brother and sister mating 
from the pure white cross produced 2 fawn colored rats, a buck and a 
doe, and 5 agoutis.^ The brother and sister mating from the Japanese 
cross produced 2 f awn-and-white Japanese, 1 cream-and-white Japanese, 

1 Italics mine. Note the reversion to full wild color. This shows the 
pink-eyed variation to be entirely different in nature from the ordinary 
albino variation. 

sNote the return of "fawn" (pink-eyed &gouti) as a recessive character 
in approximately 1 in 4 young. 



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68 THE AMERICAN NATURALIST [Vol. XLVHI 

1 black-and-white Japanese, and 4 agoutis.^ The fawns and fawn-and- 
whites resulting from these crosses were much deeper in color than the 
wild grandsire. Mated one with another they gave a proportion of 
about 2 fawn colored or fawn-and-white in 7 young.* I may say in 
conclusion that the original wild rat was in shape of body, skull, etc., 
as the ordinary brown or agouti rat that we have running wild in 
this district. 

Mr. Marriott sold a ** fawn-and-white" (pink-eyed 
hooded agouti) bnck to Mr. E. F. Tilling, of Hessenford, 
who also ** originated '^ the second variation, the ** black- 
eyed yellow," or true yellow variation. His results from 
the pink-eyed variation confirm those of Mr. Marriott. 

Mr. Tilling writes under date of October 18, 1913 : 

I see by Fur and Feather this week that you are interested in the 
yellow and cream varieties of rats. I am also much interested in these 
and have produced the latter variety within the last few months. We 
have 2 kinds over here, the yellow-and-white hooded with pink eyes and 
the self yellow (and cream) with black eyes. Both are quite distinct. 
The first mentioned was produced some 2 or 3 years ago. Mr. Harriott, 
of Chesterfield; bred the first I heard of from a wild caught fawn. He 
bred a couple of yellow and white hooded bucks of which Miss Douglas 
bought one and I the other. I mated miae to about 15 does of various 
colors and definite strains. He was a splendid breeder and got some very 
fine youngsters, but not one of his own color from the first cross^ I 
subsequently mated him to some of his daughters and they produced a 
good proportion of yellow-and-white young.' These are now fairly 
plentiful over here and are in the hands of several fanciers. 

Of the other kinds, black-eyed fawns and creams, the first one ex- 
hibited and from which all mine are descended, was a very fine wild 
caught, deep colored, fawn specimen. I got her partly tame and ex- 
hibited her at the National Mouse and Rat Club's annual show at Bristol 
on November 27 and 28, 1912, where she won first in the self class and 

8 " Fawn- and white Japanese'* means (to me) pink-eyed agouti with the 
"Japanese" color pattern (hooded). The formation of this class of young 
shows the hooded pattern ("Japanese") to be independent in transmission 
of the pink-eyed variation. * * Cream-and-white Japanese," I interpret as 
pink-eyed hlack (non-agouti) hooded. "Black-and-white Japanese" is the 
familiar black hooded. We should expect this mating to produce also self 
pink-eyed agouti and self pink-eyed black which are not mentioned. 

4 The Mendelian expectation is 2 in 8. 

5 Italics mine. Note again the recessive nature of the variation. 

*Not real yellow-and-white, as already explained^ but pink-eyed agouti- 
and-white or black-and-white. 



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No. 566] NEW VARIETIES OF RATS AND GUINEA PIGS 69 

was well commented upon in the fanciers' papers. From this doe I have 
built up my strain of black-eyed creams. I mated her to a self black 
buck and she bred 8 youngsters all wild colored.^ This is the only 
litter I had from her, as shortly afterward, during my illness, my man 
while transferring her from one cage to another let her get away and 
was unable to recapture her. However, I have bred from her young- 
sters, mating brother and sister, and the litters have invariably con- 
tained at least 1 fawn or cream^ each time. I have now just bred for 
the first time from the 3 first does so produced, again mating them to 
their brother and the result is litters of 7, 5 and 7, respectively, all self 
creams.® 

From the statements of Messrs. Marriott and Tilling, 
it is evident that the two variations, which they, respect- 
ively, have introduced into the rat fancy, are both reces- 
sive in heredity, as are also the three previously known 
Mendelizing color variations of rats, viz., (1) the albino 
variation (with uncolored coat and eyes) ; (2) the black 
variation (lacking the agouti ticking of the fur) ; and (3) 
the piebald ** hooded^' pattern of white and colored fur. 
Each of these is known to be an independent Mendelizing 
tmit-character. If the new variations are as supposed in- 
dependent of each other and of those previously known, 
they will make possible the immediate four-fold increase 
in number of the previously known color varieties of rats. 
If for the present we adopt a simplified terminology (as I 
have elsewhere suggested) for the different color varia- 
tions, employing small letters for such as are recessive 
in heredity, we may use the following set of symbols : 

White (albino) =w, 

Black = h, 

Hooded = h, 

Pink-eyed = p, 

Yellow = tf, 

7 This shows that the original yellow animal was potentially an agouti. 
A pair of yellows which Mr. Tilling has sent me have light bellies and I 
presume are also potentially agoutis. 

8 "Cream" here probably means yellow not transmitting agouti. It 
probably lacks the lighter belly as do yellow rabbits which do not transmit 
agouti. 

9 This shows that extracted yellows breed true to yellow. Hence the 
Tariation is recessive, as in rabbits and guinea-pigs, not dominant as in mice. 



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70 TRE AMERICAN NATURALIST [VOL-XLVHI 

By various combinations of these variations, if each is 
independent of all the others, 32 varieties become possi- 
ble. Half of these varieties will be albinos, white and so 
visibly indistinguishable. The other 16, we have reason 
to suppose, will look different from each other. Pre- 
viously we had but four of these, the first four in the fol- 
lowing list of the theoretically possible 16. 

1. Normal or wUd agouti, 

2. h black, 

3. h hooded, 

4. hh black hooded, 

5. p pink-eyed, 

6. pb pink-eyed black, 

7. ph pink-eyed hooded, 

8. pbh pink-eyed black hooded, 

9. y yellow, 

10. yh yellow black (t. e,, non agouti yellow), 

11. yh yellow hooded, 

12. yp yellow pink-eyed, 

13. yhh yellow black hooded, 

14. yph yellow pink-eyed black, 

15. yph yellow pink-eyed hooded, 

16. ypbh yellow pink-eyed black hooded. 

Varieties 1-4 have been known for some time; they 
have constituted the fancier's entire repertoire up to the 
present time. Varieties 5 and 9 have apparently arisen 
as wild sports obtained by Marriott and Tilling, respect- 
ively. By crosses these gentlemen have apparently ob- 
tained varieties 6, 7, 8, and probably 10. Varieties 11-16 
are as yet unknown, but will doubtless soon be produced. 
Corresponding with each of the 16 colored varieties, an 
uncolored one should be possible of production, which 
would transmit in crosses with any colored variety the 
characteristics indicated by its formula. Albinos cor- 
responding to colored varieties 1-4 are positively known 
to occur ; their symbols would be w, wb, wh and wbh, re- 
spectively. Symbols for the remaining 12 expected varie- 
ties may be formed in like fashion, by prefixing w to the 
combinations already given. 

All the five unit-character variations, which in different 
combinations are responsible for the color varieties of 



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No. 566] NEW VARIETIES OF BATS AND GUINEA PIGS 71 

rats, have their parallels in other mammals. Albinism 
and white-spotting (which in rats takes the form of the 
hooded pattern) are among the commonest. They occur 
in practically all mammals from mice to men. Albinism 
appears to consist in such a modification of metabolism 
that the process of pigment-formation can take place only 
feebly or not at all. That particular process which seems 
chiefly affected is the production of yellow pigment. 
Albinos, so far as I know, never produce genuine yellow 
pigment, though they may produce considerable quanti- 
ties of black or brown pigment, as in the case of the 
Himalayan rabbit. An undescribed variety of guinea- 
pig, which I obtained about two years ago in Peru, may 
bear as much black pigment in its coat as wild cavies do, 
yet it forms no yellow pigment at all. Further this varia- 
tion behaves as the allelomorph of ordinary albinism, in- 
dicating that it is probably of the same genetic character. 
For this reason we may provisionally consider the albin- 
ism of mammals as due to a loss of the ability to form 
yellow pigment. This usually, if not always, involves a 
lessened capacity to form other pigments also, so that it 
seems probable that the same chemical process, which 
produces yellow pigment as an end-product, is ordinarily 
involved also in producing the higher oxidation stages 
seen in brown and black pigment. In albinos this process 
would seem to be omitted, or to be accomplished by some 
step which does not involve the production of yellow 
pigment. 

The yellow variation is extremely common in mammals. 
Yellow varieties, which at opposite extremes of intensity 
of pigmentation are known as cream and red, occur 
among horses, cattle, hogs, cats, dogs, rabbits, guinea- 
pigs, mice and human beings. In this variation pigment 
oxidation stops at the yellow stage, usually throughout 
the coat but not in the eye. Described in negative terms 
a yellow variety is one in which black and brown are sup- 
pressed or restricted. Black and brown, though usually 
restricted to the eye in yellow varieties, may occur also in 



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72 THE AMERICAN NATURALIST [Vol. XLVIH 

small quantities in the fur. Examples are found among 
horses (bay and dun varieties), cattle (the Jersey breed), 
dogs (the common dirty yellow variety), rabbits (the 
* 'tortoise-shell'' variety), mice and guinea-pigs, and 
probably red-haired human beings also. 

Black varieties of mammals arise in two genetically 
distinct ways. One is a quantitative increase or exten- 
sion of black, the reverse of what happens in yellow varie- 
ties, so that black encroaches on regions normally yellow 
or may even obliterate them altogether. Examples are 
found in black squirrels, in which the agouti yellow tick- 
ing of the fur is almost, but not quite, obliterated by black 
pigment. But the ''black'' variation of rats, mice, 
guinea-pigs and ordinary rabbits results from a total 
loss, not a covering up, of the yellow ticking of the fur 
seen in agouti varieties. Genetically it is quite distinct 
from the other kind of black. It is a recessive variation 
and so breeds true. 

The pink-eyed variation is the rarest of all the five 
enumerated as occuring in rats. It has been known here- 
tofore only in mice, though I have recently obtained it 
also in guinea-pigs from Peru, where it seems to be well 
established. 

In this variation the capacity to form yellow pigment 
is unimpaired, but only traces of black or brown pigment 
are produced. Consequently varieties which possess the 
other genetic factors of normal yellow animals have fully 
pigmented (yellow) fur, but with very faintly pigmented 
(pink) eyes, when they possess this factor. If, however, 
they possess the other genetic factors of black, brown, or 
agouti varieties, along with this pink-eyed variation, then 
both the fur and the eyes are very faintly pigmented. 
From this results the seeming paradox that pink-eyed 
blacks are less heavily pigmented than pink-eyed yellows, 
so that in rats the fanciers have called the former 
"creams," the latter ''fawns." 

When pink-eyed animals are crossed with albinos, off- 
spring fully colored (eyes and all) result, as was first 



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No. 566] NEW VARIETIES OF BATS AND GUINEA PIGS 73 

shown by Darbishire some ten years ago. This indicates 
that the two variations are not only genetically distinct, 
bnt are physiologically complementary. The albino has 
defective metabolism for producing yellow (and in conse- 
quence brown and black also) ; the pink-eyed animal has 
the full mechanism for forming yellow, but its brown and 
black producing mechanism is defective. Together they 
possess the full mechanism of normal color production. 
Hence the reversion on crossing. 

White spotting is clearly due to neither of the above 
modifications, but to a different change in the metabolism 
so that no pigment at all is produced. For an albino rab- 
bit or guinea-pig may, as already observed, bear consider- 
able black or brown pigment, but a white spot either on 
an albino, on a pink-eyed animal, or on a fully colored 
animal is entirely devoid of pigment. The paradox of a 
white spot on an albino is obtainable by crossing a white- 
spotted colored race with an albino race, which develops 
some pigment in the fur, as for example the Himalayan 
race of rabbits and guinea-pigs. In this way English- 
marked Himalayan rabbits and spotted albino guinea- 
pigs have been produced in my laboratory. 

Postscript: While this paper was in press, Mr. Tilling, 
in reply to a further inquiry, wrote that his original black- 
eyed yellow rat was caught on a ship at Liverpool. The 
fact that the pink-eyed variety was found in the same gen- 
eral region leads him to believe that both variations were 
introduced on ships from some foreign country. It would 
be of much interest to know from what country or coun- 
tries. Any information on this point obtainable from 
rat-catchers or others would be welcome. 



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*^ DOMINANT" AND ^'EECESSIVE" SPOTTING IN 

MICE 

C. C. LITTLE, 
BussEY Institution, Habvahd University 

Intboductoby 

The inheritance of spotting has long proved of interest 
to animal geneticists. The nature of spotting is snch 
as to afford an excellent chance to observe quantitative 
fluctuation and variations of very minute size. Further- 
more, the fact that spotted varieties are found in all the 
rapidly breeding smaller domesticated mammals has led 
to a widespread investigation of its phenomena of in- 
heritance. 

One of the most clean-cut and constant types of spot- 
ting which has been studied is that of the ** hooded*' pat- 
tern in rats. This character was studied independently 
by Doncaster (1905) and by Castle and McCurdy (1907). 
All these observers agree that this form of spotting is 
due to a recessive Mendelizing unit which gives a 1:3 
ratio in crosses with self-colored races. 

In mice there has been no such well-localized pattern 
recorded and a series of spotted forms has been described 
which vary from black-eyed whites on one end of the 
series to heavily colored animals having only a few 
white hairs on the forehead or on the belly at the other 
extreme. 

Cuenot, who did considerable work on the inheritance 
of spotting in mice, came to the conclusion that spotting 
is due to a group of recessive spotting factors which he 
describes as pl,,p2, p3, p4, etc. His figures, however, 
show a single unit character difference as 3 : 1 and 1 : 1 
ratios prove. 

Up to 1908 all the spotting in mice was classed as re- 
cessive to solid-colored coat. At that time, however, 

74 



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No. 566] SPOTTING IN MICE ^ 76 

Miss Dnrham described the appearance of dominant spot- 
ting in addition to the recessive form which she also had 
experimented with* Such a dominant form of spotting 
is supposed, by Bateson, to be due to the addition of some 
factor for restriction of pigment formation in certain 
areas. This produces a dominant form of spotting as 
contrasted with the recessive type, which, he holds, is due 
merely to the loss of the **self ^* factor. 

Hagedoom (1912) gives data to show that the domi- 
nant form of spotting occurs in mice and in addition con- 
siders it as produced by a factor analogous to that which 
produces the dominant ** English'* spotting in rabbits. 

The object of this paper is to present certain evidence 
concerning the nature of dominant and recessive spot- 
ting in mice ; to discuss in its light the results of the above- 
mentioned investigations ; and to criticize one additional 
point in Hagedoom 's work with mice. 

EXPEBIMENTAL 

Materials. — ^Among several wild mice caught during 
the spring of 1911 was one individual with a white spot 
' or ** blaze** on the forehead between the eyes. This spot 

3 or ** blaze** was about one quarter of an inch in length 

and one eighth of an inch in width. This mouse, an adult 
j^ male, was transferred to a breeding cage and a series of 

/ experiments was started to* determine whether the 

''blaze** character was inherited and, if so, in what way. 
As at that time no adult wild females were available 
from unrelated stock the wild ''blaze** male (SI) was 
crossed with a female from a dilute brown race. In 
many ways this dilute brown race was the best possible 
material for such a cross. It was very closely inbred, 
being descended from a single pair of animals, progeny of 
which had been free from out-crossing for naore than a 
year. Further, it had never given, nor has it ever given 
in hundreds of young, an animal with the slightest trace 
of a spot, even on the tail, where white bands are fre- 
quently seen in wild mice. Besides this the race was vig- 
orous and active and yet easy to handle. 



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76 



THE AMERICAN NATURALIST [Vol. XLVHI 



Results 

As a result of mating SI ** blaze" with a female of this 
dilute brown race, two litters, totalling eight young, were 
produced. All these young were self-colored without a 
trace of white, and, as expected, all resembled the male in 
coat color. 

The Fi generation self s were then crossed in two ways, 
(1) inter se and (2) with animals of the dilute brown self 
race to which their mother belonged. It is hoped that a 
detailed account of all the matings made may be pub- 
lished later, but for the present purposes certain of the 
crosses under the first heading will suflSce. 

When Fi was crossed inter se, two sorts of young were 
produced, namely, those with white and those without. 
While all of the latter tyi>e may be classed as self, the 
former were of two general sorts: (1) those with a 
*' blaze '^ as large or larger than that of 81, these we may 
call ** blaze'' animals; and (2) those with only a few 
white hairs on the forehead, which we may call few white- 
haired (f.w.h.) animals. 

The exact numbers in this cross were 







0/ftpriDg 




Ptrents 


Self 


F.W.H. 


Blase 


56 X 55— 58 


11 

10 

3 


3 

13 

1 


3 


519 X58 


6 


518 X 58 


2 




24 


17 


11 



When the Fj few white-haired animals were bred to- 
gether they produced three types of young: few white- 
haired, blaze and self, as follows. 



. 


Oflbpring 


Parents 


Self 


F.W.H. 


Blaze 


3,030 X 3,028 


11 
5 


6 
6 




3,043 X 3.028 


1 




16 1 11 


1 



One further fact is also of interest. Various descendants 
of F2 ** blaze" animals, which should breed as recessives, 



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No. 566] 



SPOTTING IN MICE 



77 



have given the following resnlts. The generation num- 
bers may be disregarded as they refer to another method 
of classification. It is to be remembered that the parents 
in the tabulation given below, are all ** blaze'* in 
character. 







Yoaog Prodooed 






Genention 


BUM 


BlaMMdVeo-i 
tnl White j F.W.H. 


Mf 


ToUl 


F^ 

F4B 

F»B 

F.B 


33 

157 

70 

9 


6 
60 
53 

6 


4 

27 
5 



1 
3 




44 

247 

128 

16 


Total ' 269 


125 1 36 


4 


434 



If the ** blaze '* is a true Mendelian recessive we should 
expect all 434 offspring to have some white on them. 
The figures show that 430 of the 434 are of this type; 
that is to say, approximately 1 per cent, are self. 

It is possible to account for the occasional production 
of selfs even if the ** blaze'* character is a true recessive, 
if we supposed that there are supplementary factors 
which may influence color development; and it is quite 
conceivable that such is the case. 

The chief point of interest in the crosses given above 
is that while spotting behaves in F^ as a recessive, certain 
of the F2 spotted individuals fulfil the requirements of 
dominant spotting by producing self offspring. 

The spotting came from a single individual and can 
scarcely be considered to be of two distinct types. 

We may now consider the bearing of these results on 
the work of Miss Durham and Hagedoom. 

Miss Dukham's Results 
Miss Durham (1908) gives a detailed account of a re- 
cessive type of spotting in mice. The numbers she ob- 
tained are extensive, and the case seems well established, 
coming as it does in corroboration of the work of Cuenot, 
Darbishire and others. In the same papers she records 
the occurrence of a dominant spotted type of mice. Bate- 
son (1909), commenting on the case, compares it with the 



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78 THE AMERICAN NATURALIST [Vol. XLVm 

dominant ^^ English'' spotting in rabbits but also agrees 
that, in the case of mice, there is no criterion to enable one 
to distinguish somatically between the dominant and re- 
cessive forms. This, of course, is not the case in rabbits 
where the ** English'* pattern differs visibly from the 
''Dutch" spotting, which Hurst (1905) found to be re- 
cessive to self. Bateson also considers that the case of 
dominant spotting in mice, reported by Miss Durham, is 
the result of a different spotting factor from that pro- 
ducing recessive spotting. 

In terms of the presence and absence hypothesis this 
means that the dominant form possesses a factor for re- 
striction of pigmentation which self forms lack. This 
fact becomes of interest when Miss Durham's experi- 
mental results are closely examined. 

In the race which gave rise to the dominant spotting 
the following conditions are seen. 

A sooty yellow spotted mouse of unknown origin was 
crossed with a black-eyed white (spotted) animal (of 
Atlee's strain). Among other progeny was obtained a 
black-eyed white mouse with ''agouti ears." This 
mouse. No. 21 (spotted), was crossed with an albino (car- 
rying chocolate), No. 35, and gave among its progeny No. 
69, a black self mouse. This black animal. No. 69 was 
crossed with an albino (carrying chocolate), No. 34, and 
from these two individuals came the dominant spotted 
race. 

Now inasmuch as No. 34 and No. 35, the albinos, were 
not supposed to carry spotting, the dominant spotting 
must be considered as probably coming from No. 69, a 
black self animal. We know that this animal must carry 
spotting as a recessive character since its parent. No. 21, 
was spotted. 

If, therefore, this animal was the progenitor of the 
dominant spotted race, and if he carried a recessive spot- 
ting, as it seems certain he did, we must suppose that one 
of three things has happened to the recessive spotting 
which he carried. 



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No. 666] SPOTTING IN MICE 79 

1. It may have been completely lost, failing to manifest 
itself in his germ celk. 

2. It may have continued to exist and to be inherited 
together with the dominant type of spotting. 

3. It may have been changed to a so-called *' dominant*' 
type of spotting simply by the nature of modifying sup- 
plem^itary factors which it encountered during ontogeny. 

The first two cases necessitate the origin of the *' domi- 
nant*' spotting by a mutation in no way connected with 
the previous recessive spotting. In the first case, more- 
over, we should have to suppose the disappearance of the 
recessive spotting character in a manner entirely con- 
trary to any principle of Mendelian heredity. In the sec- 
ond case the occurrence of the two types of spotting side 
by side in the same litters of young would so complicate 
the experiments that analysis would be diflScult if not im- 
possible, on Miss Durham's results. 

There is good reason to believe that the third possible 
explanation is the correct one. It accounts for the for- 
merly *' recessive" type of spotting. It presupposes no 
fundamentally different appearance of the two types 
of spotting. Moreover, it is very probable that the al- 
bino race brings in the modifying factors necessary to 
give the apparent change in the type of spotting. The 
addition of a factor as presupposed by the presence and 
absence hypothesis is not proved by the results obtained 
nor is it necessary to account for them. 

That the presence and absence hypothesis does not 
apply to all cases of spotting is seen in the case of the 
** blaze" mice in my experiments. Here, if Fi animals 
had been given me as a starting point for experimenta- 
tion, I should conclude the spotting to be recessive, while 
if Fj spotted animals were given as a starting point the 
conclusion would be inevitable, that spotting should be 
considered dominant. Yet it is one and the same spot- 
ting in both cases. It is certain that ''self" and ''blaze" 
are alternative conditions, but it is equally certain that 
they differ from each other rather as two degrees of a 



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80 THE AMERICAN NATURALIST [Vol. XLVIH 

single process, one greater, the other less, than as the 
presence and absence of one or more unit characters. 

Hagedoobn's Wobk 

Hagedoorn's work shows the danger of the modem 
tendency to produce factors upon the slightest provoca- 
tion. While adding, in experimental work, only a single 
litter of young bearing on the problem, he gives a symbol 
for a factor for dominant spotting in mice, and further 
considers it as due to a factor similar to that producing 
the dominant ** English" spotting of rabbits. He refers 
to Morgan's work with black-eyed white and self mice 
as being a study of this dominant factor in mice. Mor- 
gan himself suggests that if black-eyed white mice repre- 
sent the extremes of the spotted series the appearance 
of spotted animals in crosses with selfs is due to a 
strengthening of the spotting factor or to a change in 
dominance. This is far different from supposing the 
addition of an entirely new inhibiting factor comparable 
to the English pattern in rabbits. Cuenot with mice and 
Castle (1905) with guinea-pigs have shown that black- 
eyed whites are the extreme of the recessive spotted 
series and it is almost certain that Morgan's explanation 
of the results, as due to a change in dominance, is the 
correct one. It is, of course, obvious that the presence 
and absence hypothesis fails to explain any change of 
dominance of a single character. 

To treat '^dominant" spotting in mice as due to the 
presence of a definite unit-character is exceeding present 
experimental facts, while to consider it similar in nature 
to the ^* English" spotting of rabbits is still less justified. 

One other point in Hagedoorn's work is of such a 
nature as to require further experimentation before it 
can be accepted. 

This is the case (on page 126) of ^^mutual repulsion be- 
tween two factors." In this case, Hagedoom mated to- 
gether agouti animals heterozygous in factor A (for color 
production) and in factor G (for the agouti pattern). 



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No. 566] SPOTTING IN MICE 8 1 

Such animals would ordinarily form gametes AG, Ag, aO 
and ag in equal numbers. These by independent recom- 
bination would form 

1 AAGG 

2 AaGG I 

4 AaGg . 



1 aaGG ^ 

2 aoGg I 
1 aagg J 



4 albino. 



But Hagedoom gives figures which show that the pro- 
portion which he obtains is nearer 2 agouti ; 1 black and 
1 albino. This he supposes to be due to the fact that A 
and G can never go into the same gamete. 

Now let us see what happens if this is the case. The 
original heterozygotes will form only two kinds of gam- 
etes instead of four, these will be aG and Ag. Now in the 
recombination of these gametes the following result will 
be obtained. 

1 oG aG=:l albino, 

2 oG Ag = 2 agouti, 
1 AgAg = l black. 

So far, so good, but the trouble comes in testing the 
albinos. Here I may quote from Hagedoom, p. 126 : 

. . . thirteen of these albinos have been tested by mating with black. 
Without exception they have given black or equal numbers of black 
and albino young. . . . But never has one of those albinos produced 
a single agouti young in a mating with black. Counting together the 
colored young of such families I get 89 black young?- 

This result is indeed remarkable, for on Hagedoom' s 
own hypothesis the albinos should have produced in such 
matings nothing hut agouti young, '^ since they are all, 
by his hypothesis, homozygous for the agouti factor. 
The evidence is incontestable ; no repulsion of A and G 
can have occurred. Has there been any coupling of these 
two factors! If such was the case only gametes AG and 



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82 THE AMERICAN NATURALIST [Vol. XLVm 

ag would have been formed and this would have given 
only agoutis and albinos in a 3 :1 ratio, while Hagedoorn 
reports **73 agouti, 37 blacks^ and 32 albinos/' 

The case then is nothing so simple as ^* repulsion'* or 
** coupling,'' it includes failure to segregate and com- 
plete disappearance of a dominant Mendelian factor; G 
the factor for agouti. 

Since numerous investigators of color inheritance in 
mice have never found the agouti factor anything but a 
normal Mendelizing factor epistatic to black, and since 
Hagedoorn himself seems to have become mixed in his in- 
terpretation, it seems that the case proves or shows little 
until a satisfactory answer can be found to the question 
of what has become of the agouti factor. 

Conclusions 
The facts above given lead to the following conclu- 
sions : 

1. The so-called dominant type of spotting in mice does 
not differ from *^self" color by the presence of a unit 
character which ^^self " lacks. The presence and absence 
hypothesis fails to account for the shifting dominance 
seen in spotting in mice. 

2. It is misleading to describe, under the same symbol, 
the so-called ^^ dominant" spotting of mice and the Eng- 
lish spotting in rabbits. 

3. It seems probable that differences in *' dominance" 
of spotting in mice are due to modifying supplementary 
factors and such spotting might be termed *'unsup- 
pressed" and *' suppressed" spotting rather than *' domi- 
nant" and *' recessive" in the Mendelian sense. 

4. Hagedoorn 's hypothesis of repulsion between the 
color factor. A, and the agouti factor, G, is incorrect. 

November 19, 1913. 
1 Italics mine. 



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ON DIFFERENTIAL MORTALITY WITH RESPECT 

TO SEED WEIGHT OCCURRING IN FIELD 

CULTURES OF PISUM SATIVUM 

DR. J. ABTHUR HAERIS 
Cabnbgib Institution or Washington 

In two papers which have already appeared in these 
pageSy^ I have shown that for the dwarf varieties of 
Phaseolus vulgaris the mortality of apparently perfect 
seeds (failure to germinate or to complete the life cyde) 
is not random, but differential, or selective. 

It seemed highly desirable to extend these studies to 
other forms. Pisum sativum naturally occurred to me as 
affording suitable experimental material — ^both because 
of the wide range of seed characteristics and the conve- 
nience with which it may be bred. I had no pedigreed seed 
and consequently began work in the spring of 1913 with 
commercial stock. About 1,000 seeds from each of ten 
early (dwarf) varieties purchased from the Thorbum 
seed company were weighed, individually labelled and 
planted in short rows scattered over one of the fields of 
the Station for Experimental Evolution. Conditions 
were not the best, and the mortality was high. 

Table I^ gives the weights in units of .025 gram range' 

1 Harris, J. Artbnr, "On Differential Mortality with Bespeet to Seed 
Weight Oeenrring in Field Colturee of Fhaseolus vulgaris," Amsb. Nat., 
46: 512-525, 1912; < ' Sapplementary Studies on the Differential Mortality 
with Bespeet to Seed Weight in the Germination of Garden Beans/' Amsb. 
Nat. [in press]. 

2 For conyenienee the series may be designated bj letters: A, Witham 
Wonder; B, American Wonder; C, Premiam Qem; D, Little Gem; E, Nott's 
Excelsior; F, Sutton's Excelsior; O, Laztonian; H, little Marvel; /, Peter 
Pan ; /, English Wonder. 

> Glass 1 = 0.00(K025 gram, . . . class 4 = .07&-.100, dass 5 = .100- 
.125, and so on. Thus to obtain means or standard deviations of weights in 
grams, deduct .5 from the values in the tables and multiplj bj .025. 

88 



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84 



THE AMERICAN NATURALIST [Vol. XLVHI 



TABLE I 
Weight of Seeds which Geeminated 



Series 4 



8 



10 



11 12 18 14 15 I 16 17 18 19 20 ToUls 



A 
B 
C 
D 
E 
F 
O 
H 
I 
J 



65100 
40107 
63 117 173 
36 106 191 



76 
134 



4gi05 
9 27 



107,126 



105 
63 
27 

116 
16 

142 



67 

170 

126 

167 

68 

96 

71 

183 

26 

112 



42 

105 

56 

80 

32 

86 

114 

161 

61 

41 



19 
36 
11 
18 
3 
69 
159 
63 
88 
13 



2 — 

1 



11 4 
Bl 23 

6 2 
26101 

2 — 



17 



468 
604 
549 
606 
367 
391 
631 
603 
633 
665 



TABLE n 
Weight op Seeds which Failed to Gekminatb 



Series 



8 



10 11 12 IS 14 16 



16 17 



18 



19 I 20 ToUls 



A 
B 
C 
D 
E 
F 
O 
H 
I 
J 



63 102 
2 



66 
37 
116 
13 
6 
17 
13 
66 



90 

52 

116 



88127 

210180 

46 84 

61 29 



93 78 

104;117 

122 95 
93 



91 

125 

43 



42 
84 
34 
37 
23 
153 



16 
36 
18 
11 
4 
114 



2 1 — 
3—2 

4l 1 



66, 71|110 



76 86 
93! 29 



26 35 
125; 91 



66162 

2 — 



3 

7 - 



31 



22 3 



I 



656 
400 
461 
399 
637 
613 
376 
404 
374 
439 



of the seeds which germinated.^ Table II gives the same 
distributions for the seeds which failed to germinate. 
The physical constants*^ with their probable errors are 
given in Tables III-IV. 

Taking the differences, germinated less failed, in order 
to have the positive sign if elimination tends to increase 
mean weight or variability of weight and the negative 
sign if it tends to decrease these constants in the popula- 
tion of seeds which grow as compared with those which 
fail, I find the differences shown in Table V, 

4 When the plantlets were about three inches high the labels for seeds 
which had failed to germinate were collected. The distributions for the seeds 
which had germinated were then obtained bj subtraction from the weight 
seriations prepared before planting. Some of the plants subsequently died. 

B Sheppard 's correction was applied to the second moments. 



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No. 566] 



DIFFERENTIAL MORTALITY 



85 



TABLE in 
Physical Constants tob Qxedb whiob Gbionatid 







SUndard DotUUod and 


Coeffloient of Variation 


SariM 


Mmui And Probable Error i 


Frobabla Error 


and Probabla Error 


A 


9.2541^.062 


2.000*. 044 


21.610*. 498 


B 


10.581^^.038 


1.371*. 027 


12.954*. 256 


C 


10.078*. 037 


1.294*. 026 


12.844*. 266 


D 


10.355^.033 ; 


1.211*. 023 


11.692 *.230 


E 


9.790*. 042 1 


1.193*. 030 


12.185*. 308 


F 


11.568 *.054 I 


1.671 *.038 


13.583*. 334 





13.090*. 043 1 


1.612 *.031 


12.313*. 237 


H 


11.186 *.037 1 


1.362*. 026 


12.178*. 240 


I 


14.269*. 057 


2.134*. 041 


14.958*. 290 


J 


9.773*. 040 


1.429*. 029 


14.622*. 300 



TABLE rV 
Physioal Constants fob Skeds which Failed to Gbionatk 



Seriw 


Mean and Probable 


Standard DoTlation and 


Coefficient of Variation 




Error 


Probable Error 


and Probable Error 


A 


8.993*. 057 


2.003*. 041 


22.286*. 472 


B 


10.898*. 041 


1.236*. 030 


11.346 *.274 


C 


9.913*. 045 


1.439*. 032 


14.512*. 829 


D 


10.048*. 041 


1.229*. 029 


12.234*. 296 


E 


9.488*. 030 


1.122*. 021 


11.826*. 227 


F 


11.726*. 045 


1.653*. 032 


14.097*. 277 





12.816*. 062 


1.787*. 044 


13.945*. 350 


H 


10.869*. 049 


1.447*. 034 


13.317*. 322 


I 


13.225*. 089 


2.552*. 063 


19.298*. 493 


J 


10.009*. 044 


1.376*. 031 


13.749*. 311 



TABLE V 
CoicPABisoN OF Physical Constants fob Skkdb Gkbminatino with those 

FOB SXEDS FaILINO TO QlBMINATB 





Difference In Mean 


Difference In Standard 


Difference in Coefficient 


Series 


and Probable Error of 


DoTiation and Probable 


of Variation and Probable 




Difference 


Error of Difference 


Error of Difference 


A 


+ .261*. 085 


-.003*. 060 


-1.676*. 686 


B 


- .316*. 067 


+.134*. 040 


+1.608*. 375 


C 


+ .165*. 068 


-.144*.041 


-1.669*. 423 


D 


+ .307*. 063 


-.019*.037 


- .642*. 375 


E 


+ .302*. 051 


+.071*. 036 


+ .358*. 382 


F 


- .158*. 070 


-.082*. 049 


- .513*. 434 





+ .274*. 075 


-.175*. 054 


-1.632 *.422 


H 


+ .317*. 062 


-.085*. 044 


-1.139 *.401 


I 


+1.044 *.105 


-.418*. 074 


-4.340*. 572 


J 


- .236*.060 


+.053*. 042 


+ .873*. 432 



Consider first the differences in the mean weight. 
Seven are positive and three are negative. All of the 



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86 THE AMERICAN NATURALIST [VoL-XLVHI 

seven positive differences are at least 2.5 times their prob- 
able error; four of them are over five times their prob- 
able error. The mortality is therefore almost certainly 
selective, with a tendency to leave the surviving popula- 
tion with seeds distinctly heavier on the average than 
those which were planted. On the other hand, there are 
the three cases in which the seeds which produced plant- 
lets were on the average lighter than those which failed 
to germinate. One of these differences is only 2.2 times 
its probable error, and so perhaps not statistically trust- 
worthy. Of the other two, one is over 5.5 times and the 
other nearly 4 times its probable error. There can be 
little doubt that in at least one of these cases there is a 
tendency for the lighter seeds to show a viability greater 
than that of the heavier. In garden beans, too, strong 
evidences of differences between strains in this regard 
have been pointed out. 

The interpretation of the variabilities offers greater 
diflSculties than does that of the means. More data and 
more refined methods of analysis are necessary for a final 
solution of the problem. It appears, however, that in 
seven of the ten series the variability of the seeds which 
survived is less than that of those which failed. This is 
true whether absolute variability as measured by the 
standard deviation or relative variability as expressed 
by the coeflScient of variation be used in the comparison. 

As far as these data go, therefore, they are in general 
accord with those for Phaseolus. In both of these Legu- 
minosae the mortality which occurs before germination is 
not random but differential. But in both cases, and espe- 
cially in Pisum where the seeds used are of commercial, 
not pedigreed, stock and number as yet only about 10,000, 
far wider series of experiments and much refinement of 
methods of analysis are necessary to establish fully the 
nature and the immediate (physical or chemical) cause of 
this selective death rate. 

Cold Spring Hasbor^ N, Y., 
July 28, 1913 



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THE INHERITANCE OF A EECURRING SOMATIC 

VARIATION IN VARIEGATED EARS 

OFMAIZE^ 

PROFESSOR R. A. EMERSON 

UNiyEBsrnr of Nsbraska 

Intbodtjotion 

The inheritance of variegation has special interest and 
importance in genetics. It is with forms of variegation 
that the only two certainly known cases of non-Mendelian 
inheritance have had to do. I refer to Banr's experiments 
with Pelargonium, in which crosses of green-leaved and 
white-leaved forms exhibited somatic segregations in Fj 
that bred tme in later generations, and to Correns^s work 
with Mirabilis, which showed green and white leaf color, 
to be inherited through the mother only. De Vries^s con- 
ception of *' ever-sporting '* varieties was apparently 
fomided largely upon the behavior of variegated flowers 
in pedigree cultures, from which he reached the conclusion 
that the variegated color pattern and the monochromatic 
condition arising from it as sports are non-Mendelian in 
inheritance. Correns, however, has shown that in Mira- 
hilis jcUapa the inheritance of these sports is distinctly 
lifendelian, and the results of East and Hayes indicate the 
same for Zea mays. In this paper I shall present data 
from maize and attempt to show how they can be inter- 
preted in strictly Mendelian terms. 

Variegation is distinguished from other color patterns 
by its incorrigible irregularity. It is perhaps most often 
seen in the coloration of flowers and leaves but also occurs 
in fruits, seeds, stems, and even roots of various plants. 
It is characteristic of the ears of certain varieties of maize 
known, at least in the Middle West, as ^ ^ calico ' * com. In 

iThe experimental results reported here were presented at the Cleveland 
meeting of the American Societj" of Naturalists, January, 1913. Besearch 
l)Qlletin No. 4 of the Nebraska Agricultural Experiment Station. 

87 



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88 THE AMERICAN NATURALIST [Vol. XLVni 

these varieties the pericarp of most of the grains has f ew 
to many narrow stripes of dark red, the remaining area 
being colorless or showing a sort of washed-out red. 
Often broad red stripes appear on some grains, a single 
stripe covering from perhaps one tenth to nine tenths of 
the grain. Not uncommonly there are entirely colorless 
grains (so far as pericarp is concerned) and also solid red 
grains scattered over the ear. Much more rarely there 
is found a **freak*^ ear with a large patch of self -red or 
nearly self-red grains. Or sometimes an ear is composed 
largely of red or almost red grains with a small patch of 
striped or nearly colorless grains. In such cases it is not 
uncommon for the margin of the red area to cut across a 
grain so that one side — always the side toward the red 
patch — ^is red and the other side colorless or striped. Ears 
that are colorless throughout, except for a single striped 
grain, are not unknown and there are even known ears 
that are red except for a single striped grain. Very rarely 
a plant has one self-red ear and one variegated ear on the 
same stalk. It is also conceivable that all the ears of a 
plant might thus become red, but of course such a red- 
eared plant rising as a bud-sport could not ordinarily be 
distinguished from a red-eared plant arising as a seed- 
sport. 

Variegated ears generally have variegated cobs, the 
amount of red in the cob ordinarily varying with the 
amount of red on the grains. In some **freaks" a part 
of the cob is solid red and the rest variegated. In a few 
such cases the red part of the cob corresponds exactly in 
position to the freak patch of grains. This is more fre- 
quently true when the grains of the freak patch are dark 
variegated than when they are self-red. In other ears 
there is no change in the cob corresponding to the change 
in the grains. The husks of variegated ears are also 
rather commonly variegated. In a few freak ears the red 
side of the ear is enclosed in reddish husks, the remainder 
of the husks being light striped. Red-eared plants aris- 
ing as seed-sports always have solid red cobs and usually 
solid reddish husks. 



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No. 566] INHERITANCE IN EAB8 OF MAIZE 89 

The first account, so far as I am aware, of the inherit- 
ance of the striking somatic variations so commonly found 
in variegated plants was given by de Vries* in his dis- 
cussion of ever-sporting varieties. The study was made 
in the years from 1892 to 1896 with a variety of Antir- 
rhinum with striped flowers. De Vries^s records are re- 
produced diagrammatically in Fig. 1. 

Pi Striped 

plant 



I 

Striped Red 

plants plants 

90% 10% 



-L 



( I ( 1 

Fs Striped Red Striped R6d 

plants plants plants plants 

98% 2% 24% 76% 

I '" 1 

Striped Red 

branches branches 

i-^-. I ' 1 

Fi Striped Red Striped Red 

plants plants plants plants 

98% 2% 29% 71% 

I ^ I ^ 

F4 Striped Red Striped Red 

plants plants plants plants 

96% 5% 16% 84% 

FIO. 1. DUOBAM FBOK I« VBIBS*8 RSCOKDS SHOWING THB INHBEITANCII OF 

Yabibgation AMD Sblf-bbd IN THE Flowbrs ov Antirrhinum. 

Of these results de Vries says : 

From these figures it is manifest that the red and striped types differ 
from one another not only in their visible attributes, but also in the 
degree of their heredity. The striped individuals repeat their peculiarity 
in 90-98 per cent, of their progeny, 2-10 per cent, sporting into the uni- 
form red color. On the other hand, the red individuals are constant in 
71-84 per cent, of their offspring, while 16-29 per cent, go over to the 
striped type. Or in one word : both types are inherited to a high degree, 
but the striped type is more strictly inherited than the red one. 

De Vries 's results were in some respects very similar 
to those of Correns and it is probable that he would have 
interpreted them in the same way had he then been famil- 
iar with Mendelian phenomena. 

aVries, Hugo de, "Species and Varieties," pp. 309-328 (1905). 



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90 



THE AMEBIC AN NATURALIST [Vol. XLVm 



Correns^ has reported results of a careful study of the 
inheritance of the self -green condition appearing as a 
bud-sport on variegated-leaved plants of Mirabilis jalapa, 
and also of a self-color appearing in striped-flowered 
plants of the same species. His results for self-green 
and variegation of the leaves are shown diagranunatically 
in Fig. 2. The results are stated in approximate per- 
centages. I have seen no report in which the detailed 
records were given. 

Variegated 
plant 



I — 

Variegated 
branch 

I 



Variegated 
plants 
100-a* 



Ft 



r" 

Vgtd. 
100-a 
, I 



Green 

plants 

a 

_i 



I — 

Variegated 

plants 

25 



1 

Green 
branch 

I 



>66 
I 



<33 



r 

66 



Green 

plants 

75 

_J 



Green 
a 



Vgtd. 
25 



Green Green Vgtd. 
76 100 100-a 



Green 
a 



Vgtd. Green >66 <33 
branch branch 

V G V G V G G 



ranch I I I 



-i-^ 



Vgtd. 
25 



33 

I 



Green Green 
75 100 



x\ xx\ 



66 33 



VGVGGG VGVGG VGVGGG 



Fi 100-a a 25 75 25 75 100 100-a a 25 75 100 100 100-a a 25 75 100 100-a a 25 75 100 100 



FIO. 2. 



COBBBNS'S DIAOBAK SHOWING THB INHBRITANCB OF VABIBQATION AND 

Sblf-gbbbn in thb Lbaves of Mirabilis jalapa. 



The diagram shows that a variegated branch of a varie- 
gated plant produces in F^ mainly variegated plants, but 
occasionally a wholly green plant, while a green branch 
from the same plant produces in Fj 25 per cent, varie- 
gated and 75 per cent, green plants. The Fj variegated 
plants, however produced, behave in later generations 
just like the original variegated parent plant. The Fi 
green plants, whether produced from green or variegated 
branches, are always of two sorts, namely, those that are 
homozygous and therefore breed true green, and those 

• Correns, C, Ber, Deutsch, Bot. Gesel, 28: 418-434, 1910. Der Uher- 
gang aua dem homoeygoiischen in einen heteroeygoiischen Zustand im selben 
Individuum hei hunihlditrigen wnd gestreifihlUhenden MirdbUia-Sippen, 

* Numerals indicate approximate percentages; a =0-10 per cent. 



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100 



No. 566] INHERITANCE IN EAB8 OF MAIZE 91 

that are heterozygous and therefore produce progenies of 
green and variegated individuals in a ratio of approxi- 
mately 3 to 1. Correns points out that a green branch of 
a variegated plant behaves as though it belonged not to a 
variegated plant at all, but to a hybrid between a varie- 
gated plant and a green one, in which green is dominant, 
and that half of the germ cells produced by the green 
branch carry a factor for green and the other half a factor 
for variegation. Similar results were secured from 
branches with self-colored flowers on plants with striped 
flowers, except that such branches produce few if any 
more self-colored plants than are produced by branches 
with striped flowers. Plants with self-colored flowers, no 
matter how they arise, behave as they would if they had 
occurred in an Fj progeny of a cross of striped by self- 
colored plants. 

Results of Experiments with Maize 
Hartley* in 1902 gave an account of an experiment with 
variegated maize. In a comparatively pure white strain, 
which occasionally produced a red ear, there was found an 
ear similar to some of the *' freak '^ ears noted earlier in 
this paper. It is described as being red except for a spot 
covering about one fifth of the surface, in which the grains 
were white with fine red streaks. The excellent plate ac- 
companying the account, however, shows that most of the 
**red'* grains had white streaks at the crown and that the 
cob was light-colored, not red. From the near-red grains 
of this ear there was produced a crop of 84 red ears and 
86 pure white ones^ while from the variegated grains of 
the same ear there came 39 light variegated ears and 36 
white ones. Hartley refers to the parent ear as a ' ' sport 
or sudden variation from the type*' but does not indicate 
whether the *Hype'' in mind was the white variety or the 
red ears occasionally produced by it. Both the color of 
the grains and cob and the production of about 50 per 
cent, of white ears from both the red and the variegated 
grains indicate very clearly that the parent ear was a 

* Hartley, C. P., Yearbook, U. S. Bept. Agr., 1902: 543-544. 



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92 THE AMERICAN NATURALIST [Vol. XLVIII 

heterozygous, variegated one and that it probably came 

from a white seed crossed by a stray grain of pollen from 

a variegated-eared plant, just as the occasional red ears j 

in the white variety were certainly produced by stray pol- ' 

len from red-eared plants. 

More recently East and Hayes^ reported like behavior 
of a similarly variegated ear. An ear having on one side 
solid red grains and on the other white and very light j 

variegated grains, similar to some of the ''freak'' ears 
noted earlier in this paper furnished the material for the 
test. The ear was produced from a white seed in a field 
of otherwise pure white corn and was therefore doubtless 
heterozygous for pericarp color and was probably pol- 
linated in large part from plants without pericarp color, 
so that 50 per cent, white-eared plants were to be expected 
in its progeny. The white, the light variegated and the 
solid red grains were planted separately. The white and 
the variegated seeds alike produced light variegated and 
white ears, 15 of the former and 15 of the latter. The red 
seeds produced 22 white ears and 22 solid red ears. The 
authors' interpretation of these results is that the white 
seed which gave rise to the original colored ear had been 
fertilized by pollen from a red-eared plant and that the 
Fi plant, ''due to produce a red ear varied, somatically so 
that one half of the ear was red and one half striped." 
The authors further state : 

This variation was transmitted by seeds, but at the same time the 
hybrid character of its seeds was unchanged as shown by their segrega- 
tion into reds and whites in the next generation and the normal segre- 
gation of the hybrid dark reds in a further generation. 

In the light of my own observations, it is equally pos- 
sible and seems more likely that the white seed from which 
the original red-and-variegated ear came was the result 
of pollination from a plant with variegated ears, and that 
the somatic variation was from variegated grains to solid 
red grains rather than from red to variegated. But the 
important fact is that a somatic variation was later in- 
herited in a strictly Mendelian way. 

5 East, E. M., and Hayes, H. K., Bui. Conn. Agr. Expt. Sta., 167: 106-107. 
1911. 



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No. 566] 



INHERITANCE IN EARS OF MAIZE 



93 



In 1909 I obtained results somewhat similar to those re- 
ported by East and Hayes. A few ''freak" ears were 
secured, mainly from local and national com expositions. 
Nothing was learned as to their parentage or pollination. 
Obviously, however, the parentage of the red, the varie- 
gated, and the white grains of any one ear was the same, 
and it is reasonable to suppose that the different sorts of 
grains of any one ear were pollinated with approximately 
the same kind or the same mixture of pollen. The results, 
as shown below, were essentially like those of Hartley and 
of East and Hayes. 





Number of Plants with 




Seed! PlftDted 


Red Ears 


Variegated Eari 




White Ears 


Self-red 


43 








33 


Variegated and white 


22 




29 



The results from four other ears were somewhat differ- 
ent, probably owing to differences in their pollination. 
(See Fi^. 3.) They were as follows: 



Flo. 3. A, •' freak " ear of maize ; B, progeny of striped seeds ; C, progeny of 

self-red seeds. 



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94 



THE AMERICAN NATURALIST [Voi.. XLVHI 





Number of Plants with 


Seed! Planted 


Red Ears 


Variegated Ears 


White Ears 


Self-red 


128 
8 


32 
103 


69 


Variegated and white 


68 



Two other ears of similar history, while they gave quite 
as striking results as those noted above, probably do not 
belong here since none of their immediate progeny were 
variegated and no variegated ears have occurred in later 
generations. These two ears were made up of red grains 
and white grains only. The results were as follows : 



Seeds Planted 
Red.... 



Number of Plants 
Red Ears White Ears 



rw- 



White. 



.77 
. 



85 
122 



The white ears bred true in later generations and the 
red ears produced reds and whites in typical Mendelian 
fashion. No such somatic variations as these have oc- 
curred in my cultures of self-red or white maize, so that I 
have been unable to study them further. Somatic varia- 
tions in variegated corn, however, are not rare. Unfor- 
tunately several of the most pronounced of those occur- 
ring in my cultures were open-pollinated and therefore 
of little or no use in a careful study. I have therefore 
been obliged to make use in large part of the few solid 
red and nearly solid red grains scattered over otherwise 
more or less evenly variegated ears. 

From twenty-three self-pollinated, variegated ears of 
plants that were homozygous for pericarp color, grains 
with various amounts of red were selected and planted. 
The results are summarized as follows : 





Namberof Plants with 


Seeds Planted 


Self-red Ears 


Variegated Ears 


Non-red Ears 


Self-red 


8 
56 

9 

5 
33 

1 


9 
16 
34 
22 
394 
22 





Nearly self-red 





More than half red 

Less than half red 






Narrow red stripes 





Non-red 






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No. 566] 



INHERITANCE IN EAB8 OF MAIZE 



95 



Besides these 23 ears, 20 other selfed ears from homo- 
zygous plants contained only narrow-striped seeds from 
which there were produced 16 plants with red ears, 280 
with variegated ears, and none with white ears. Similarly 
21 selfed ears with narrow-striped seeds only, from plants 
that were heterozygous for pericarp color, produced 28 
plants with red ears, 411 with variegated ears, and 208 
with non-red* ears. Variously colored grains from 42 
self-pollinated, heterozygous, variegated ears gave the 
following results : 





r Namber of Planti with 


Seeds Planted 


Self-red Ears 


Variegated Ears 


Non-red^ Ears 


Sdf-red 


15 
17 
46 

8 
67 




1 

8 

51 

34 

767 

10 


6 


Neariy self-red 


8 


More than one half red 

Narrow red strioes 


31 

21 

300 


Non-red 


6 



In the progenies of these 63 self-pollinated ears that 
were heterozygous for pericarp color, there were approxi- 
mately 2.5 plants with pericarp color to one without it. 
All the classes of grains from self -red to non-red yielded 
both colored and non-colored ears, thus indicating, as 
already shown by East and Hayes, that the somatic varia- 
tion in the seeds does not change their hybrid character. 
Considering only the plants with pericarp color, in the 
progenies of both heterozygous and homozygous varie- 
gated ears, 106 progenies in all, marked differences are 
seen in the percentages of self-red ears from seeds of the 
different color classes, as follows : 

« Some of these ears had what I have termed ^' half -red" pericarp, i. e., 
periearp with a reddish color extending part way from the base to the 
crown of the seeds. (See Ann. Bpt. Nebr. Agr. Expt. Sta., 24: 62. 1911.) 
Half-red differs from self -red and variegated red not only in distribution 
but also in almost never developing f uUy in the heterozygous condition. It 
is hypostatic to self -red, but shows between the red stripes of variegated 
seeds. Since its pr^ence does not mask either self -red or variegated-red 
and since it is strictly allelomorphic to both of them, half -red is here in- 
cluded with non-red. Variegated ears have never, in my observation, pro- 
duced half -red grains aa somatic variations. 

T Some of these were half -red. See footnote 6.) 



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THE AMERICAN NATURALIST [Vol. XLVm 





Number of PUnU with 


Per Cent Self-red 
AmongColored 


SeeaaFUnted 


Self-rMl Ears 


Variegated Ears 


Self-red 


23 
73 
55 
13 
134 
1 


10 
24 
85 
56 
1.852 
32 


69.7 


Nearly self-red 


75.3 


More than one half red 

Leas than one half red 

Narrow red stripes 


39.3 

18.8 

6.7 


Non-red 


3.0 



In comparison with the cases reported by Hartley and 
by East and Hayes and one of my first cultures from 
open-pollinated ears, in all of which red grains produced 
no variegated ears and striped grains no red ones, the 
striking features of the results from these 106 self -pol- 
linated ears are the facts that the wholly red grains 
yielded some variegated as well as red ears and that the 
striped grains and even the wholly non-red grains yielded 
some red as well as variegated ears. The percentages noted 
above indicate in a general way that for self -pollinated, 
variegated ears, the more red there is in the seed planted 
the larger the percentage of red ears in the progeny. 
These records, however, do not give a wholly trustworthy 
indication of the mode of inheritance of the somatic vari- 
ations concerned here. If there is a modification of some 
factor in the female gametes, associated with a visible 
modification of somatic cells of the pericarp and even at 
times of the cob and husks, modifications that do not be- 
come visible until long after the gametes are formed, may 
there not be a similar modification of the same factor in 
the male gametes, though here not associated with any 
visible change in somatic cells because of the fact that the 
staminate inflorescence dies too soon after the pollen is 
shed? If male gametes do carry such modified factors 
and if the modification is as irregular in occurrence as the 
somatic modifications seen in variegated ears, so that any 
part of the tassel, from all to none, may produce gametes 
with the modified factor while not showing any visible 
somatic modification, it is obvious that the real nature of 
the male gametes of any variegated-eared maize plant 
can not be foretold. The mere fact that a variegated ear 
is self-pollinated, therefore, does not insure that its seeds 
are fertilized with pollen of known character. 



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No. 566] INHERITANCE IN EARS OF MAIZE 97 

That the male gametes of variegated-eared maize do 
often carry factors for self-red is shown by crosses of 
pure non-red strains with pollen from plants with varie- 
gated ears. The plants that furnished the pollen for 
these crosses were in some cases the same ones whose self- 
pollinated ears were concerned in the records discussed 
above. The results of these crosses are summarized here. 
Eight non-red ears crossed by plants that were homozy- 
gous for pericarp color yielded 17 red-eared, 116 varie- 
gated-eared and 8 white-eared® plants. Similarly, 14 ears 
of pure non-red strains crossed by pollen from plants 
heterozygous for pericarp color yielded 26 red-eared, 192 
variegated-eared and 229 white-eared plants. Consider- 
ing merely the plants with colored ears, 22 crossed ears 
produced 43 red-eared to 308 variegated-eared plants, or 
a little over 12 per cent, self-red. 

Since the male gametes of variegated-eared com have 
now been shown occasionally to carry a factor for self- 
red, it is obvious that only from crosses of variegated- 
eared plants with pollen from pure non-colored strains, 
can a definite idea of the inheritance of the somatic varia- 
tions in pericarp color be gained.* Twelve ears from 
homozygous, variegated plants cross-poUinated by non- 
red strains might have afforded important evidence, but 
for the fact that 7 of them contained only narrow-striped 
grains and the other 5 no fully or even nearly self-red 
grains. The results are summarized here : 





Namberof Plants with 


Seeds Planted 


Self-red Ean 


Variegated Ean 


Non-red Ean. 


More than one half red 

Less than one half red 

Narrow red s^pes 


5 

2 



11 

15 

281 

22 







Non-red 














< Some of the 8 white ears may have been extreme light tjpes of varie- 
gation, for in some other cases very light variegated and wholly white ears 
have been observed on the same plant. And of course some of them may 
have been due to accidental pollination of the parent ear. 

• Though the genetic factors for pigment patterns in maize seem to be 
distinct from the factors for the pigment concerned in these patterns, no 
non-colored maize that I have used has ever given any indication in crosses 
of carrying pattern factors. 



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98 



THE AMERICAN NATURALIST [Vol. XLVHI 



The principal facts of interest here are the production 
of only one red-eared plant to about 140 variegated-eared 
ones from narrow-striped seeds, and of about one red- 
eared to two variegdted-eared plants from seeds with 
from one half to perhaps three fourths red. 

Of 20 variegated ears, heterozygous for pericarp color, 
that were crossed with pollen from pure non-colored 
strains, 5 had only narrow-striped grains and 15 had 
variously broad-striped grains and even some self-red 
ones. The summaries of these crosses are as follows : 





Number of Plmnts with 


Seeds Planted 


Self-red Ears 


Variegated Ears 


Non-red Ears 


Self-red 


9 
5 
4 
3 

7 





2 
5 
265 


11 


Nearly self-red 


2 


More than one half red 

Less than one half red 

Narrow red stripes 


2 

9 

301 


Non-red 


27 


20 



Here again, just as with homozygous, variegated ears, 
the more red there is in the pericarp the more likely are 
the female gametes to carry a factor for self -red. While 
the number of individuals dealt with are too few to aflford 
reliable evidence, it is suggestive to note that the ratio of 
red-eared to variegated-eared plants, though not the ratio 
of red-eared to total plants, is greater in case of parent 
ears that are heterozygous than of those that are homozy- 
gous for variegated pericarp. 

So far nothing has been said of the results in genera- 
tions later than the one grown from the selected seeds 
(Fi). Let us now see what results follow when the varie- 
gated ears and the red ears produced as explained above 
become the parents of second generations (Fg) from the 
selected seeds. The variegated ears so produced behave 
like the original variegated ears from which seeds were 
selected and their progenies have, therefore, been included 
in the data already presented. There remains only to 
present the records of the progenies of red ears. 

Data are available from 7 Fi red ears obtained from 
self -pollinated, homozygous, variegated plants. Five of 



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No. 666] 



INHERITANCE IN EARS OF MAIZE 



99 



these red ears were self -pollinated and two were crossed 
with pure white-eared plants. The results in F, and Fg 
were as follows : 





KumberofFluitswith 


Seeds PlAiiUd from 


Self-red 
Esn 


Ysriecmted 
Een 


Kon-red 
Ears 


Fi redfl from selfed, homo., vgtd. Pi's 
5 wiTfl jwlf^yl 


119 
46 

9 
16 

26 
40 


37 
45 

2 
• 








2 ears X white 





Fs reda from self ed Ft reds 
1 ear i»lf«l 





1 ear selfed 





Fs rods from Fi rods X white 
1 ear selfed 


5 


2 ears X white 


37 



The above is approximately what would have been ex- 
pected, had the F^ red ears that arose from self-polli- 
nated, homozygous, variegated-eared plants been pro- 
duced by a cross between red-eared and variegated-eared 
races. 

Of the Fj reds arising from self-pollinated, heterozy- 
gous, variegated-eared plants, nine were selfed and two 
were crossed with whites. The results secured in Fj and 
Fo follow: 



Seeds Planted from 


Self-red 
Eurt 


Variegsted 
Ears 


Non-red 
Ears 


Fi rods from selfed, hetero., vgtd. Pi's 
3 eara selfed (a) 


104 

6 

106 

12 

59 
23 


23 
7 



12 






1 ear X white 





6 earo selfed 


38 


1 ear X white 


7 


Fs rods from selfed Fi rods of (a) 
4 eara selfed 





1 ear selfed 






From the above it api)ears that the F^ red ears, arising 
from self-pollinated, heterozygous, variegated-eared 
plants behave in some cases as if they were hybrids be- 
tween red-eared and variegated-eared races and in other 
cases as if they were hybrids between red-eared and 
white-eared races. 

Of the four possible sorts of red-eared ** sports*' from 
variegated-eared plants, two remain to be treated. Be- 



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100 



TEE AMERICAN NATURALIST [Vol. XLVm 



cause of their similar behavior they will be considered 
together here. Of the Fj red ears arising from homozy- 
gous, variegated-eared plants that had been crossed with 
white-eared races, three were self-pollinated and two 
crossed with whites. Of the Fi red ears arising from 
heterozygous, variegated-eared plants that had been 
crossed with white-eared races, four were selfed. The 
results in Fg and F3 are : 



Seeds Planted from 


Self-red 
Ears 


Variegated 
Ears 


NoD-red 
Ears 


Fi reds from vgtd. Pi's X white 
Pi's homozygous 

3 ears selfed 


54 
34 

102 

32 
43 











16 


2 ears X whites 


43 


Pi's heterozygous 
4 ears selfed 


47 


Fi reds from selfed Ft reds 

3 ears selfed 


10 


1 ear selfed 






So far as these results go they indicate that F^ reds 
arising from crosses between both homozygous and heter- 
ozygous, variegated-eared plants and white-eared races 
behave as if they were hybrids between red-eared and 
white-eared races. 

One homozygous, variegated-eared plant was cross- 
pollinated by a homozygous red race. From the varie- 
gated ear produced, self-red, nearly self-red, and narrow- 
striped seeds were planted. All resulted, of course, in 
red-eared Fj plants, 16 in all. A self-pollinated Fi red 
ear from a narrow-striped seed gave in F2 24 red-eared 
and 11 variegated-eared plants — somewhat fewer reds 
than were to have been expected. An Fi red ear from a 
nearly self-red grain, when cross-poUinated with non-red, 
yielded 9 reds and 11 variegated in Fg. A third Fj red- 
eared plant, this one from a self-red grain of the varie- 
gated parent ear, bred true red in Fg. One ear of this Fj 
plant was selfed and yielded 14 reds in Fg, and another 
ear was cross-pollinated by non-red and yielded 29 reds. 

There are various other somatic variations rather fre- 
quently seen in maize, but they are apparently not in- 



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No. 566] INHERITANCE IN EARS OF MAIZE 101 

herited. There are sometimes found variegated ears 
with a large patch of self-red cob but with little or no cor- 
responding change in the color of the overlying grains. 
I have as yet no evidence that this somatic variation in 
cob color is inherited through the seeds of the self-red 
part of the cob. Such seeds apparently always produce 
ears with variegated grains and variegated cobs, just as 
do other seeds of the same parent ear. Of course varie- 
gated seeds from a self -red patch of cob occasionally give 
rise to a self -red ear, as discussed in detail in this paper, 
and such red ears always have self -red cobs, but this is 
also true of all self -red ears, whether or not they are pro- 
duced by red or by variegated seeds and without respect 
to whether the part of the cob underlying these seeds is 
self-red, finely variegated, or entirely white. 

Another form of somatic variation seen in ears of maize 
is the occurrence of patches of considerable size, the 
grains of which, though variegated, are much darker in 
color than the grains of the rest of the ear. Such patches 
of grains are often quite as strikingly distinct in appear- 
ance as patches of self-red grains, and are apparently 
even more likely to correspond exactly in outline with an 
underlying patch of self-red cob than are patches of self- 
red grains. Moreover, such dark, variegated grains often 
present a rather definite color pattern. The crowns are 
often made to appear almost solid red by the widening 
and convergence at the crown of narrow red stripes ex- 
tending down toward the base of the grain particularly on 
the side opposite the germ. Another type of dark, varie- 
gated grains differs from the lighter, variegated grains 
of the same ear principally in the greater development of 
the somewhat washed-out red apparently underlying the 
dark red stripes of the variegation pattern proper. I 
have grown numerous progenies from dark and light 
variegated grains of the same ears, but as yet have no 
evidence that such somatic variations are inherited. Not- 
withstanding this, I have strains of maize breeding true 
to a very dark type of variegation, others to a medium 



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102 THE AMERICAN NATURALIST [Vol. XLVm 

sort of variegation, and still others to exceedingly light 
types of variegation. There can be no doubt that some of 
these different types of variegation are inherited, bnt the 
mode of inheritance in crosses has not been fully worked 
out. 

One other form of grain coloration that might be called 
an extremely dark type of variegation is to be noted. The 
grains are self-red throughout except for a nearly color- 
less crown formed by converging light stripes extending 
some way down the side of the grain opposite the germ, 
almost exactly the reverse of one of the types of dark 
variegation described above. Variegations of this sort 
behave in inheritance almost exactly like fully self-red 
grains, giving a large percentage of red-eared prog^iy. 
And these red ears are apparently always fully self-red, 
never showing the pattern of converging light lines seen 
in the parent seeds. Many such seeds have been included 
in the results recorded earlier in this paper where they 
were listed as ** nearly self-red.** 

Intebpbbtation of Besults 
Anyinterpretation of the data presented here must take 
account of these facts: (1) that the more red there is in 
the pericarp the more frequently do red ears occur in the 
progeny, and (2) that such red ears behave just as if they 
were Fj hybrids between red and variegated or red and 
white races. The development of red in the pericarp is 
evidently associated with and perhaps due to a modifica- 
tion of some Mejidelian factor for pericarp color in the 
somatic cells. The zygotic formula of a plant homozy- 
gous for variegated i)ericarp may be designated as W, 
and that of a plant heterozygous for variegated pericarp 
as V — . If in any somatic cell VV, from unknown causes, 
a V factor were transformed into a factor for self -color, 
8, that cell would then have the formula VS. Any peri- 
carp cells descended from it would without further modi- 
fication be red. If all the pericarp cells of a seed were 
thus descei^ded, the seed would be self -red, just as it would 



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No. 666] INHERITANCE IN EARS OF MAIZE 108 

if the plant bearing it were a hybrid between pure red and 
vari^ated races. Moreover, one half of the gametes 
arising from such somatic cells wonld carry V and one 
half would carry 8, just as if the plant were a hybrid of 
red and variegated types. Or, if both V factors were 
changed, the grains would be self-red as before, but all 
instead of half the gametes would carry S. If, however, 
the modification from VV to V8 should occur very early 
in the life of the plant, or even of the embryo, all the ears 
of the plant might thereby become self -red, and one half 
of all the gametes both male and female might then carry 
8 and the other half F as in the ordinary hybrid. Or the 
plant might then become a sectorial chimera with one 
variegated ear and one red ear, the gametes from the one 
side of the plant all carrying V. If the modification 
occur much later, say soon after the ear begins to form, 
there might then be merely a solid patch of red grains on 
an otherwise variegated ear. In this case only those 
gametes arising from these smaller masses of tissue would 
carry half 8 and half F. If, however, the modification 
occur after the grains begin to form, the latter might be 
perhaps three fourths red, or one half red, or merely have 
narrow stripes of red, depending upon the amount of peri- 
carp directly descended from the modified cell. In this 
case it seems reasonable to assume that the larger the 
mass of modified tissue the greater the chance that the 
gametes concerned should carry 8. Finally, if in certain 
grains the change never occurs, they should show no red 
and the gametes formed in connection* with them should 
all carry F, none 8. 

Similarly, it may be assumed that in any cell of a heter- 
ozygous, variegated-eared plant, F — , the F factor may 
as before become an 8 factor. The effect on pericarp 
color would be exactly the same as in a homozygous, vari- 
egated plant, and, of the gametes arising from the modi- 
fied tissue, one half would carry iS^ as in the other case, 
but the other half, instead of carrying F, would carry no 
factor and would be represented by — . 



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104 THE AMERICAN NATURALIST [Vol. XLVIH 

If the interpretation suggested here is correct, it is to 
be expected that the more red there is in the pericarp of 
any seeds, i. e., the larger the mass of tissue descended 
from the cell in which the change from V to S took place, 
the greater the chance that the female gametes concerned 
carried the factor S. With heterozygous, variegated- 
eared plants, V — , however, never more than half of the 
gametes concerned could carry S even in case of self-red 
grains, the other half of the gametes carrying no factor, 
— . Of the heterozygous, variegated ears the progenies 
of which have been reported here, some were self ed, some 
crossed with white, and some open-pollinated. From self- 
pollinated ears, self-red and nearly self-red seeds yielded 
32 red-eared, 9 variegated-eared, and 14 non-red-eared 
plants, or practically 58 per cent, self-red. This excess of 
self-red ears may be due, in part at least, to the presence 
of the S factor in some of the male gametes concerned, but 
the numbers are too small to give very reliable indica- 
tions. From similar ears that instead of being selfed 
were crossed with white, so that the results could not have 
been influenced by factors present in the male gametes, 
self-red and nearly self -red seeds produced 14 plants with 
red ears and 13 with non-red ears, or about 52 per cent, 
red. While these numbers are very small, the fact that 
no variegated ears were produced, but that every ear with 
any red color was self-red, is noteworthy. From the 
open-pollinated, heterozygous ears included in my cul- 
tures self-red seeds gave progenies consisting of 171 red- 
eared, 32 variegated-eared, and 102 non-red-eared plants, 
or about 56 per cent. red. 

In case of homozygous, variegated-eared plants, VV, all 
the gametes associated with seeds that later become self- 
red could carry /S only if both V factors of the somatic cells 
from which the gametes arise were changed to S factors. 
Because of the rarity of changes from V to S, unless both 
V factors are influenced alike by whatever causes the 
change, so that both change simultaneously to S factors, 
the chance is slight that more than one will ever change. 



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No. 566] INHERITANCE IN EARS OF MAIZE 106 

In the latter case only about 50 per cent, of the gametes 
associated with self-red grains of homozygous, varie- 
gated ears could be expected to carry S, just as in the 
case of heterozygous ears. None of the open-pollinated 
ears whose progenies I have grown were homozygous for 
variegated pericarp, and none of the homozygous ears 
that had been crossed with white contained any self red or 
nearly self -red seeds. The only data, therefore, that bear 
upon the point at issue are those obtained from self -pol- 
linated, homozygous, variegated ears. The self -red and 
nearly self-red seeds of such ears produced 64 red-eared 
and only 25 variegated-eared plants, or about 72 per cent, 
self-red. This may mean that in some cases both V 
factors were changed to S factors, but the results may 
just as likely be due to the presence of S in an unusually 
large percentage of the male gametes concerned. The 
production of the 25 variegated-eared plants, however, is 
very good evidence that, in at least a very considerable 
number of cases, not more than one of the two V factors 
could have been changed to S. 

If the change from F to iS^ should happen to occur at such 
a time that the grain rudiments became sectorial chimeras 
consisting of say one half modified cells and one half un- 
modified ones, one half of the pericarp would be expected 
to show red color and the other half no color. It would 
be expected further that the chances of a particular 
gamete's arising from a modified or from an unmodified 
ceU would be equal. If then one half of the gametes asso- 
ciated with these one-half -red grains arise from cells in 
which only one of the V factors has been changed to S, 
one fourth of the gametes should carry S and three 
fourths should carry F, or one f ourth S', one fourth F, and 
one half — , depending upon whether the ears concerned 
are homozygous or heterozygous for variegated pericarp. 
Such grains from homozygous ears should, therefore, 
whether selfed or crossed by white, yield about one red 
ear to three variegated ones. Similarly, from hetero- 
zygous ears, grains with one half their pericarp red should 



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106 THE AMERICAN NATURALIST [VOL.XLVm 

yield about one red to two variegated to one white if self- 
pollinated and one red to one variegated to two white if 
crossed by white. (This is on the assumption that no S 
factors are carried by the male gametes.) Let us assume 
that by lumping together all the seeds listed in the fore- 
going records as *^more than one half red*' and as *4ess 
than one half red'* the whole lot would average about one 
half red, and compare the results with the expectation as 
noted above. From grains of these two classes from 
homozygous ears both selfed and crossed by white, there 
resulted 19 red-eared and 82 variegated-eared plants, or 
a ratio of about 1:4.3 instead of 1:3. From heterozy- 
gous ears self-pollinated grains of these two classes 
yielded 54 red-eared, 85 variegated-eared, and 52 white- 
eared plants, and similar grains crossed by white yielded 
7 red-eared, 7 variegated-eared, and 20 white-eared plants, 
or ratios of 1.04:1.63:1 and 1:1:2.86 instead of 1:2:1 
and 1:1:2, respectively. The observed ratios are cer- 
tainly suggestive but must not be given undue importance, 
for there is no assurance that the seeds used really aver- 
aged one half red and no assurance that some of the male 
gametes in the case of the selfed seeds did not carry S. 

We must now examine the results secured in genera- 
tions later than F^, and note whether the hypothesis under 
consideration applies equally well to them. 

It will be recalled that Fj red-eared plants that arose 
from homozygous, variegated ears which had been self- 
pollinated (see page 99) yielded in Fa only red-eared and 
variegated-eared progeny. On our assumption the for- 
mula of the parent variegated ears was VV, but the red 
grains of these ears were VS and the gametes associated 
with them therefore either V or S or all S. Female 
gametes carrying S would have produced red. ears in Fj 
whether the male gametes carried S or V, and female 
gametes with V could not have produced red ears except 
when the male gametes uniting with them carried S. The 
Fi red-eared plants must therefore have been VS or S8, 
the former being expected much more frequently than the 



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No. 566] INHERITANCE IN EARS OF MAIZE 107 

latter, owing to the rarity of S' in male gametes. Only 7 
such red ears were tested and all yielded red and varie- 
gated ears in typical Mendelian ratios, showing that all 
of them were V8 like any Fi hybrid between red and 
variegated races. Of two Fj reds from self ed Fi *s, one 
again yielded reds and variegates and one apparently 
bred true red. Three Fj reds, from Fj reds crossed by 
whites, yielded reds and whites only— typical Mendelian 
results throughout. 

When Fj red-eared plants arose from either homozy- 
gous or heterozygous, variegated ears that had been cross- 
pollinated by whites they yielded only red-eared and 
white-eared, never variegated-eared, offspring (see page 
100), just as if they were Fi ears of a cross of reds with 
whites. By hypothesis the parent variegated-eared plants 
were V — -and VV, and their red grains 8 — and 8V (or 
possibly 88). The gametes associated with such grains 
were therefore 8 and — , and 8 and V (or possibly all iS). 
The male gametes from white races were all — . The Fi 

plants were therefore 8 — , V — , and , only those with 

8 — having red ears. The five red-eared Fi plants that 
were tested produced in Fj red-eared and white-eared 
plants in Mendelian ratios. Of the Fg red-eared plants 
one bred true in Fj and three again segregated into reds 
and whites. 

When heterozygous, variegated, parent ears were self- 
pollinated, the Fi red-eared plants behaved in some cases 
like hybrids of red with variegated races and in other 
cases like hybrids of red with white races (see page 99). 
Our assumption is that the variegated-eared parent plants 
were V — and their red grains 8 — . The gametes asso- 
ciated with these red grains were of course 8 and — . The 
male gametes of the same plants were doubtless largely 
V and — y though a few were probably 8. The Fj plants 

must therefore have been , V — , 8 — , 8V or 88. Reds 

with 88 would be expected only rarely, and of the 11 Fj 
reds tested none had that formula, else they would have 
bred true in Fj. Seven of the 11 Fi reds evidently were 



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108 TBE AMEBIC AN NATURALIST [VouXLVm 

8 — , for they yielded Fg progenies consisting of reds and 
whites only. Four of the 11 were obviously 8V, for they 
yielded Fg's of reds and variegates only. Of the latter 
Fg reds, one bred tme in F3 and four again segregated 
into reds and variegates. 

From a self -red seed of a homozygous, variegated ear 
that had been cross-pollinated by a pure red race, an F^ 
red-eared plant was produced and this plant bred true red 
in Fg. From a nearly self-red seed of the same varie- 
gated, parent ear, an Fj red was produced but yielded 
reds and variegates in Fg just as did a similar Fj ear 
from a seed with narrow red stripes (see page 100). The 
variegated parent ear was VV and the red and near-red 
grains probably VS. The gametes associated with these 
grains were V and S. The male gametes were all S. 
Therefore the Fg reds were in part V8 and in part 8S. 

By way of summary, it is recalled that, in all, 28 Fj red- 
eared plants were tested by Fg progenies. Only one of 
these bred true and that one came from a red grain of an 
ear that had been cross-pollinated by a pure red race. 
Disregarding the three Fg red-eared plants thus produced 
and the 9 red ears produced from seeds of variegated ears 
that had been cross-pollinated by white races and that 
therefore could not have bred true, there remain 16 F^ 
reds, none of which bred true in Fg. Had these Fj red- 
eared plants behaved as did the F^ green-leaved plants 
produced by green branches of variegated-leaved parents 
in Correns's experiments, approximately 5 of the 16 
should have bred true. It will be recalled that Correns 
found that such green branches always produced green- 
leaved and variegated-leaved plants in the ratio of 3:1, 
and that one of the three bred true and the other two 
again segregated, just as must have happened if the green 
branch had been a part of an Fj hybrid of green with 
variegated instead of a part of a homozygous variegated 
plant. 

The difference between Zea and Mirabilis is, however, 
not a fundamental one, but is due merely to the circum- 



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No. 566] INHERITANCE IN EARS OF MAIZE 109 

stance that MirabUis has perfect flowers while Zea is 
monecious. In MirabUis both male and female gametes 
of a green branch arise from somatic cells in which the V 
factor has changed to a G factor. If a change in only one 
V factor is responsible for the production of the green 
branch, the somatic cells of such a branch must all be VG 
and the results reported hj Correns are the only ones to 
be expected. With Zea mays, however, all the grains of 
one ear of a variegated-eared plant might arise from cells 
having V8, so that half of the female gametes would carry 
S, while little or no corresponding change might take 
place in the staminate inflorescence and therefore no (or 
very few) male gametes would carry 8. From such an 
ear of maize only about one half, instead of three fourths, 
of the Fj plants should have red ears and none (or very 
few), instead of one third, of the Fj plants should breed 
true. 

The occasional green plants {^'a" per cent.) arising 
from variegated branches in Correns 's experiments with 
MirabUis are more nearly comparable to Fj red-eared 
maize plants than are the green plants arising from green 
branches. It is quite conceivable that on a variegated 
branch the male gametes might arise from cells that are 
VG, while the female gametes arise from cells that are 
VV, or the reverse, though this difference between male 
and female gametes would hardly be so common an occur- 
rence as with maize where the staminate and pistillate in- 
florescences are situated so far apart. It is worthy of 
note in this connection that of the occasional green plants 
produced by selfed seed of variegated plants in Correns *s 
experiments with MirabUis (see diagram, Fig. 2), less 
than one third bred true and more than two thirds segre- 
gated into green and variegated. (Correns indicates this 
merely by the signs < and > in connection with 33 per 
cent, and 66 per cent, respectively, in his diagram, and 
gives no indication of how much less than 33 per cent, 
bred true or how much more than 66 per cent, segregated.) 

De Vries's results with Antirrhinum yield readily to 



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1 1 THE AMERICAN NATURALIST [Vol. XLVin 

the same analysis used with Zea and Mirabilis. Selfed 
seed from striped-flowered branches gave a small per 
cent. — ^from 2 to 10 — of red-flowered plants. Only a few 
of the red-flowered plants were tested and these were 
found to yield 76 per cent, red to 24 per cent, striped. 
Selfed seed from red-flowered branches of striped-flow- 
ered plants yielded 71 per cent, red-flowered and 29 per 
cent, striped-flowered plants, approximating the 75 per 
cent, and 25 per cent, indicated by Correns^s results with 
Mirabilis. None of these red-flowered plants bred true, 
but only one test, and that of only a few plants, was made. 
The results were 84 per cent, red-flowered and 16 per cent, 
striped-flowered plants. It seems quite likely that had 
de Vries tested more red-flowered plants he would have 
found some of them to breed true. 

Correns ^s results with striped and red flowers of Mirdb- 
His differed in one impK)rtant respect from his results 
with variegated and green plants of the same species, as 
well as from the principal results with Zea reported here 
and from de Vries 's results with striped-flowered and red- 
flowered forms of Antirrhinum. When red-flowered 
plants arose from striped-flowered varieties of Mirabilis, 
they behaved just as did the green plants that arose from 
variegated forms. But selfed seeds from wholly red- 
flowered branches of otherwise striped-flowered plants 
yielded little if any larger percentages of red-flowered 
plants than did selfed seeds from striped-flowered 
branches of the same plants. It would seem that in case 
of Mirabilis flowers, when the self pattern arises as a 
somatic variation from the variegated pattern there is no 
corresponding change in the Mendelian factors for these 
patterns. In case of seed-sports from variegated-flow- 
ered to red-flowered plants, however, the factors for vari- 
egation are affected just as in case of green plants arising 
from variegated ones and of red-eared maize plants aris- 
ing from variegated-eared ones. The apparently non- 
inherited somatic variations of maize plants, noted briefly 
earlier in this paper, are possibly of the same nature as 



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No. 566] INHEBITANCE IN EARS OF MAIZE 111 

the somatic variations in variegated flowers of Mirabilis. 
Some of these variations in maize are self -red cob patches 
on otherwise variegated cobs^ and dark, variegated grains 
occurring in patches or scattered over light, variegated 
ears. 

Gbnbbal Considbrations 

The experiments of de Vries, Correns, Hartley, and 
East and Hayes, as well as the records reported in this 
paper, all indicate that certain somatic variations are in- 
herited in strictly Mendelian fashion. All these somatic 
variations consist in the appearance of self-colors on 
plants that are normally variegated in pattern. The fact 
that variegated plants occasionally throw both bud-sports 
and seed-sports with self -colors is not, in general, to be 
taken as an indication that the variegated plants in ques- 
tion are heterozygous. Such behavior seems to be insep- 
arably associated with variegation. Coi'rens has pointed 
out {loc. dt.) that variegated MirahUis plants can not be 
considered mosaics of green and **chlorina** tyi)es due to 
heterozygosis, since they do not segregate into chlorina 
and green, but into variegated and green. The same rea- 
soning applies to variegation in the color of maize ears. 
Variegated-eared plants do not throw reds and whites, but 
reds and variegates. The conclusion seems irresistible 
that self-color occurring as a somatic variation is due to 
the change of a Mendelian factor for variegation into a 
factor for self -color. If this be granted, the behavior of 
these variations in later generations is a mere matter of 
simple Mendelian inheritance. 

From the title of his paper and the tone of his discus- 
sion, it is clear that Correns regards, as the most signifi- 
cant feature of these inherited somatic variations, the 
change from a homozygous to a heterozygous condition. 
He even refers to them as cases of **vegetativen Bastar- 
dierung'^ or *'autohybridization.** To me, however, the 
essential feature is the change of one Mendelian factor 
into another. The fact that this modification of genetic 
factors results in a change from homozygosis to heterozy- 



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112 THE AMERICAN NATURALIST [Vol. XLVIH 

gosis seems wholly incidental. It follows from the circum- 
stance that usually only one of the two V factors of so- 
matic cells is modified. My own data do not in fact show 
that the change always affects only one of the factors at a 
time. While the results prove that this is true in a part 
of the cases at least, the Fj ratios suggest the possibility 
of both factors being modified in some cases. 

It is of course utterly impossible at the present time to 
conceive of the cause or even of the nature of this change 
in factors from V to 8. We can only conjecture at pres- 
ent as to whether the change may possibly be associated 
with changing metabolic processes in the maturing plant, 
or perhaps be connected in some way with changing ex- 
ternal infiuences, or even be a quality inherent in the V 
factor itself. It is perhaps significant that in maize, at 
least, the change, whatever its cause, occurs very rarely 
early in the life of the plant and apparently becomes in- 
creasingly more frequent as the plant matures. Wholly 
red ears in variegated-eared plants are extremely rare; 
large patches of red grains are somewhat less rare ; indi- 
vidual red grains occur on most variegated ears; red 
stripes on the individual grains are very frequent, in fact 
all but universal in some strains, though in other strains 
— ^very light variegated ones — ^there may be only a few 
striped grains on a whole ear, the others being wholly 
colorless. As a matter of fact, even the presence of an 
ear with red pericarp throughout on a variegated-eared 
plant may not be good evidence that the change in factors 
occurred before the ear began to form. If the change 
took place before the ear was laid down, it would seem 
that the cob should always be self -red, since the red-eared 
progeny of such modified grains of the variegated parent 
plant invariably have red cobs, and cob and pericarp 
colors are coupled absolutely in later generations. But 
red ears, or nearly red ears, with light variegated instead 
of red cobs, have been found to occur as somatic variations 
on variegated-eared plants. Such behavior suggests that 
sometimes the factor change may occur almost simul- 



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No. 566] INHEBITANCE IN EABS OF MAIZE 113 

taneously in the rudiments of every grain so that the 
grains become self-red while the cob remains variegated. 
We might, of course, account for the appearance of self- 
colored grains on a variegated cob on the basis of sepa- 
rate factors for cob and pericarp color^® by the assump- 
tion that one of these factors may be modified while the 
other remains unchanged. But we should then have the 
no less difficult problem of accounting for the universal 
appearance of red cobs with Fj red ears without respect 
to whether the parent grains stood on red or variegated 
cobs." 

Forced to its logical limit, our conception of the V f ac-, 
tor is that of a sort of temporary inhibitor, an inhibitor 
that sooner or later loses its power to inhibit color devel- 
opment, a power that once lost is ordinarily never re- 
gained. Of course it may be that there is present in varie- 
gated maize merely a dominant factor for self -color, 8, that 
is temporarily inactive, but that sooner or later becomes 
permanently active. Even if this be true, S as an active 
factor and /S as an inactive factor are certainly as distinct 
in inheritance as they are in development and therefore 
deserve to be designated separately. And since in one 
case there results self -color and in the other variegation, 
the factors may as well be called 8 and V as anything else. 
It is of course also conceivable that the 8 factor may re- 
peatedly arise de novo, though this seems very unlikely. 

Whatever our conception of the nature of the factors 
for variegation and for self-color in maize ears, these 
factors are certainly as distinct in inheritance as any two 
factors could well be. Moreover, there is abundant evi- 
dence, which can not be given here, that they are strictly 
allelomorphic, as indeed they must necessarily be if one 
arises by modification of the other — this on the assump- 
tion that the factors are definitely localized in certain 

10 Evidence that there are distinct factors for cob and pericarp color was 
presented in a previous paper on coupling and allelomorphism in maize. 
Ann, Bpt. Nebr. Agr. Expt. Sta., 24: 59-90. 1911. 

11 This problem is discussed in another paper on the simultaneous modifi- 
cation of distinct Mendelian factors. Ameb. Nat., 47: 633-636. 1913. 



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114 THE AMERICAN NATURALIST [Vol. XLVm 

chromosomes. Furthermore, these factors are to be re- 
garded as pattern factors. Though they must influence 
the development of the pigment in order to produce a pat- 
tern at all, they are now known to be distinct in inherit- 
ance from the factors for pigment — a fact that I have 
been able to show by use of a race of maize with a peculiar 
brown pericarp in addition to races with red pericarp. 

SUMMABY 

A somatic variation in maize is shown to be inherited in 
simple Mendelian fashion. The variation has to do with 
the development of a dark red pigment (or in one stock 
a brown pigment) in the pericarp of the grains, often 
associated with the development of an apparently similar 
pigment in the cob and husks. 

Plants in which this pigment has a variegated pattern 
may show any amount of red pericarp, including wholly 
self-red ears, large or small patches of self-red grains, 
scattered self-red grains, grains with a single stripe of 
red covering from perhaps nine tenths to one tenth of the 
surface, grains with several prominent stripes and those 
with a single minute streak, ears with most of the grains 
prominently striped and ears that are non-colored except 
for a single partly colored grain, and probably also plants 
with wholly self-red and others with wholly colorless ears. 

It is shown that the amount of pigment developed in the 
pericarp of variegated seeds bears a definite relation to 
the development of color in the progeny of such seeds. 
This relation is not such that seeds showing say nine 
tenths, one half, or one tenth red will produce or even tend 
to produce plants whose ears as a whole or whose indi- 
vidual grains are, respectively, nine tenths, one half, or 
one tenth red. Experimental results indicate rather that 
the more color in the pericarp of the seeds planted the 
more likely are they to produce plants with wholly self- 
red ears, and, correspondingly, the less likely to yield 
plants with variegated ears. 

Self-red ears thus produced are shown to behave in in- 



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No. 566] INHEBITANCE IN EABS OF MAIZE 115 

heritance just as if they were hybrids between self-red 
and variegated races or between self-red and non-red 
races, the behavior in any given case depending upon 
whether the parent variegated ears were homozygous or 
heterozygous for variegated pericarp and whether they 
were self-pollinated or crossed with white. 

It is suggested that these results may be interpreted by 
the assumption that a genetic factor for variegation, V, 
is changed to a self -color factor, 8, in a somatic cell. All 
pericarp cells directly descended from this modified cell 
will, it is assumed, develop color, and of the gametes aris- 
ing from such modified cells one half will carry the S 
factor and one half the V factor if only one of the two V 
factors of the somatic cells is changed, or all such gametes 
will carry 8 if both V factors are changed. 

The V factor is thought of as a sort of temporary, re- 
cessive inhibitor that sooner or later permanently loses 
its power to inhibit color development, becoming thereby 
an S factor. Or it may be that the dominant factor, 8, 
is temporarily inactive, but sooner or later becomes per- 
manently active. Again, the 8 factor may repeatedly 
arise de novo. The cause of any such change in factors 
is beyond intelligent discussion at present. 

Tie results of Correns with Mirabilis and of de Vries 
with Antirrhinum are shown to be subject to the same 
analysis as that used to interpret the results secured with 
maize. 



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EESTOEATION OF EDAPHOSAUEUS CRUCIGEB 

COPE 

Professoe E. C. case 
University of Michigan 

In the year 1882 Cope described from the Permian beds 
of Texas, an imperfect reptilian skull which he called 
Edaphosaurus pogonias. Two years later he described 
for the first time, the wonderful vertebra with elongate 
spines bearing lateral projections on the sides. These 
verteibraB he assigned to the same genus as the skull but 
later they were removed to a separate genus as he con- 
sidered that the two specimens represented different 
forms of reptilian life. The vertebrae with long spines 
and cross pieces were placed in the genus Naosaurus — 
** Ship-lizard,*' a name suggested by the fancied resem- 
blance of the spines with their lateral projections to the 
masts and yard-arms of a full-rigged ship. 

From the time of the original description until 1907 the 
two genera were regarded as distinct but in that year 
Case^ suggested that the two genera should be united and 
that the skull described as Edaphosaurus by Cope be- 
longed with the vertebral column and limb bones de- 
scribed under the name Naosaurus. The similar condi- 
tion of elongate spines, but without cross pieces, on the 
vertebrae of the carnivorous genus Dimetrodon very nat- 
urally led to the belief that the two forms Edaphosaurus 
and Dimetrodon were similar in other parts of the body 
and Naosaurus merely exhibited something of the extrav- 
agance in spines, rugosities, tubercles, etc., which is such 
a common feature in the most highly specialized members 
of any group which is approaching the final stages of its 
family or generic life. The close relationship of the two 
genera was so probable that it was accepted by all paleon- 

1 Publicatioii 55, Carnegie Institutioii of Washington. 

117 



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118 THE AMERICAN NATURALIST [Vol. XLVm 

talogists and even Case was very reticent in his sugges- 
tion that they were much farther apart than was usually 
thought. Following the generally conceived idea of Nao- 
saurus a composite mount was prepared in the American 
Museum of Natural History in New York in which the 
skull and limb bones of a Dimetrodon were associated 
with the vertebral column of a Naosaurus. This restora- 
tion was published by Dr. Osborn in the Bulletin of the 
American Museum and a model of the creature in the 
flesh was prepared under his direction by Mr. Chas. 
Knight. Case in his ** Revision of the Pelycosauria of 
North America" republished this restoration by Osborn 
but at the same time published an alternative restoration 
in which the skull described as Edaphosaurus was asso- 
ciated with the vertebral column of Naosaurus and the 
two genera were united under the former name, as it had 
priority. 

T^he composite restoration prepared at the American 
Museum has gained wide circulation in the text books but 
later discoveries have shown that it was unfortunate. In 
the summer of 1911 Dr. B . v. Huene, of Tiibingen, while 
a guest of the joint expedition from the universities of 
Chicago and Michigan to the Permo-Carboniferous beds 
of New Mexico, discovered the remains of a skeleton of 
Edaphosaurus in which both the skull and a portion of 
the vertebral column were preserved. As the vertebrae 
bore the typical cross-pieces of the genus Naosaurus the 
identity of the two genera was established but new evi- 
dence was speedily coming; Case in the summer of 1912 
discovered in the Permo-Carboniferous beds of Archer 
County, Texas, the nearly perfect vertebral column of an 
Edaphosaurus (Naosaurus) cruciger Cope with the limb 
bones, and a crushed skull, identical with the skull origin- 
ally described as Edaphosaurus. 

From this skeleton, now preserved in the museum of 
the University of Michigan, the author has prepared the 
restoration shown in B ig. 1. The only conjectural parts 
are the size of the feet and the length of the tail ; the re- 



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No. 566] EDAPH08AUBUS CBUCIGEB 119 

mainder is based upon careful measurements from a 
single specimen. So far from being a carnivorous, rap- 
torial animal similar to Dimetrodon, Edaphosaurus was 
harmless, moUuscivorous or insectivorous with possibly 
some ability to masticate vegetable matter. The edges 
of the jaws were lined with sharp conical teeth and upon 
the palate and the dentary bones were strong plates sup- 
porting numerous blunt, conical teeth. The head in all 
specimens recovered seems rather small for the size of 
the body and in this is peculiar in the Permo-Carbonif- 
erous reptilian fauna, in which the reverse is the rule. 
The shape of the head in the restoration is taken from the 
nearly perfect and undistorted skull in the museum of the 
University of Chicago. The elevated dorsal spines begin 
with the third vertebrae and speedily reach a considerable 
height. The lateral projections are elongate at the base 
of the spine but above the middle are reduced to mere 
nodules irregularly arranged. The author is not in ac- 
cord with the suggestion made by Jaekel and Abel that 
the spines were separate, and can see no reason for the 
suggestion made by the former that the spines were mov- 
able. The strongly interlocking zygapophyses render such 
an idea impossible to any one familiar with the skeleton. 
Nor does the author believe that the spines were of any 
use to the creature as offensive or defensive weapons; 
rather, as he has frequently expressed himself, he believes 
that they were in the nature of excessive growths which 
may have had their inception and impetus in some useful 
function, but grew beyond that use as the animal became 
more specialized. The union of the spines into a thin 
dorsal fin is far more probable and the idea is supported 
by the presence of rugosities and the channels of small 
nutrient vessels such as would lie beneath a thick dermal 
covering. The anterior and posterior faces of the bases 
of the spines have sharp, low ridges which give place to 
shallow grooves farther up the spine ; only near the top 
are the spines similar on all sides. Moreover in the liv- 
ing genus Basiliscus, which has elevated dorsal spines. 



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120 THE AMERICAN NATURALIST [VOL.XLVin 

and in the genera of the chameleons in which the same 
thing occurs, for example, Chameleo cristatus Stutch., the 
spines are united into a thin dorsal crest by the integu- 
ment and are further united by a thin membrane carry- 
ing scattered muscle fibers. The outline of the dorsal 
fin shown in the restoration is suggested by all the speci- 
mens in which the spines have been preserved. The sharp 
recurvature of the spines in the lumbar region is less 
pronounced in the specimen from which the restoration 
was drawn than in some other and it is possible that in 
other species there was even more of an overhang of the 
posterior end. The spines are abruptly shortened in the 
pelvic region and rapidly decrease on the tail. The length 
of the tail is not known but in all probability was elongate 
rather than short and stumpy. 

The limbs were short and heavy with the forearm and 
foreleg shorter than the proximal segment of the limb, a 
condition which is quite common in slow moving forms or 
those of aquatic or palustrial habit, and just the reverse 
of the condition found in the active, raptorial Dimetro- 
don. The bones of the feet have not been found in posi- 
tion, but in the great Brier Creek Bone-bed in Archer 
County, Texas, excavated by an expedition from the Uni- 
versity of Michigan in the summer of 1913, numerous 
large foot bones of a character different from those of 
Dimetrodon or the cotylosaur Diadectes were found as- 
sociated with the spines of Edaphosaurus and with large 
claws. It is believed that the foot of that animal was of 
goodly size and armed with sharp claws well fitted for 
digging in the soft earth or vegetation, tearing open rot- 
ten logs and overturning rocks in search of food. 

It has been noted by all collectors in the Texas beds that 
isolated vertebrae of Edaphosaurus are among the most 
common fossils found but that any portion of an asso- 
ciated skeleton is extremely rare. This has led to the 
suggestion that the remains of the animals were trans- 
ported for some distance after death, probably by rivers 
from a higher land. 



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No. 566] EDAPE08AURUS CBUCIGEB 121 

Edaphosaurus was a highly specialized creature, slug- 
gish in movement and entirely harmless, living upon mol- 
luscs, insects and perhaps vegetation. It probably lived 
in the woods or near swamps at some distance from the 
lowlands upon which were deposited the deltas which 
make up the Wichita and Clear Fork formations. 

In conclusion the author wishes to express his thanks to 
Dr. Euthven, of the University of Michigan, for many 
valuable suggestions in arranging the pose and propor- 
tions of the restoration, and to Mr. Irwin Christman, of 
the American Museum, for the painstaking care with 
which his suggestions have been followed in making the 
drawing.2 

s A full aceonnt of the known tpedmens of Edaphotaurui and NaoiauruM 
and a complete Bynonjmj of the two genera will be found in Publications 
55 and 181 of the Carnegie Institution of Washington. 



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SHORTER ARTICLES AND DISCUSSION 

HTOIIDITY— A NEGLECTED 'FACTOR IN ENVIRON- 
MENTAL WORK 

An admittedly rough but probably fair estimate of the relative 
interest which has been taken in the relation of the various 
environmental factors to insects, at least, may be made from the 
fact thart; Bachmetjew in his admirable compilation^ of the work 
along these lines devotes, in round numbers, four hundred pages 
to temperature, one hudred and fifty to food and chemicals, 
seventy to light, forty-five to humidity, fifteen to electricity and 
magnetism and thirty to mechanical and other factors. Why is 
it that temperature is given about a third more attention than all 
the other factors put together? Is it true that it is nearly ten 
times as interesting or important as humidity ? 

A partial answer to the first question undoubtedly is that tem- 
perature is easily controlled as well as measured, whereas humid- 
ity, for example, is not easily controlled and the means of 
measuring humidity in small containers are untrustworthy and 
expensive. Furthermore, work with temperature gives results. 
The unfortunate part is that these results have usually been as- 
cribed wholly to temperature. 

In the course of some work at the Carnegie Station for Ex- 
perimental Evolution I found that I could change to a surprising 
extent the markings on the larvae of a moth {Isia isabella) by 
varying the temperature at which they fed and moulted. How- 
ever, such changes were much more definite when the tempera- 
ture was kept constant and humidity varied. I did not have the 
necessary apparatus for getting accurate control of either factor, 
but I feel confident that temperature had little or no direct in- 
fluence. It was acting through its influence upon humidity. . 

It would seem unnecessary to urge upon experimenters such a 
fundamental principle in the logic of cause and effect, but the 
fact is that with only two or three exceptions none of the more 
than a hundred papers having to do with the effect of tempera- 
ture upon insects tell us anything about the effect of temperature 

1 * * Experimentelle Entomologische Studien vom phjsikalisch-chemischen 
Standpunkt aus. '* Zweiter Band. Sophia, 1907. 

122 



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No. 566] SHORTER ARTICLES AND DISCUSSION 1 23 

per se. A few state that the atmosphere was ** moist" or *'dry," 
but even then how moist or how dry is not usually mentioned 
unless it is believed to be saturated or absolutely free from moist- 
ure. It is clearly incumbent upon the one who makes such a criti- 
cism to show, either by his own work or in a review of that of 
others, that humidity is a factor of such importance that the 
criticism is worth the making — especially since the point is so 
self-evident and has been made in the past. The following notes 
are an attempt to justify the preceding. 

The experiments of many wofkers show that when lepidop- 
terous pupae are subjected to abnormal temperature part, at 
least, of the adults which emerge differ from the normal. The 
observations have usually been made on color changes, and 
Fisher^ especially has shown that warm conditions (36*' to 41 '^ C.) 
produce the same or similar effects as do cold conditions (O*' to 
10^ C), also that hot conditions (42** to 46^ C.) produce effects 
wliich are similar to those produced by freezing ( — 20"* to 0** C). 
Fisher apparently had no means of successfully controlling the 
humidity but Tower* claims to have had this in his ** Investiga- 
tion of Evolution in Chrysomelid Beetles of the Genus Leptino- 
tarsa" and he obtained similar results, stating them as follows: 

The result produced by either a higher or a lower temperature is the 
development of a greater amount of pigmentation and a consequent me« 
lanic tendency in variations. This stimulus in both directions to increased 
pigmentation reaches a maximum between 5® and 7^ C. deviation from 
normal. Beyond these, as the temperature further deviates, there is 
a rapid fall in melanism, first to the normal, and then to a condition 
below normal, until a marked albinic tendency is found; and this de- 
crease in pigmentation continues until the zero point is reached, be- 
yond which no pigment whatever is produced. The zero point is 
reached much sooner, however, in high-temperature experiments than 
in low. 

Tower then gives the results of experiments in which all the 
environmental conditions, except humidity, are '* normal.'' 
Normal humidity for Leptinotarsa decemlineata is taken as rang- 
ing from 43 per cent, to saturation with an average of 74 per cent. 
The humidity in various experiments ranges from 10 per cent, to 
saturation. The lowest natural humidity of which I have seen 
a record is 5 per cent. It occurred in Death Valley, California, 

2 866 Archiv fiir Bassen- und GeselUchafts-Biologie, 1907, IV, pp. 761- 
793, for Fisher's statement concerning criticisms of bis conclusions. 
8 Carnegie Institution of Washington, Publication No. 48, 1906. 



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124 



THE AMEBIC AN NATURALIST [Vol. XLVHI 



where the monthly means for May to September inclusive varied 
from 20 per cent, to 27 per cent. The annual mean at Cairo, 
Egypt, is 56 per cent, and at Ghardaia (Algerian Sahara) is 
50 per cent, at 7 a.m. and 26 per cent, at 1 p.m. The humidity 
at Buitenzorg, Java, during the height of the rainy season fluc- 
tuates between 70 per cent, and 97 per cent, during the day. 
Naturally, when dew is being deposited the humidity is practi- 
cally 100 per cent. It will be seen then that even Tower's ex- 
treme averages (see below) are not beyond the range of 
possibility in nature, although they are as great as it is possible 
to use in experimental work, since at an average of 34 per cent, 
humidity only 0.4 per cent, of the larvae reached the adult stage 
and atmosphere can not be kept supersaturated. 

The beetles were seriated according to an arbitrary scale in 
which '^20 equals total melanism and total albinism." It is 
difScult to suggest a better method of measuring the extent of 
melanism than this, although we could wish for diagrams to aid 
us in grasping just what the scale means. I have tabulated the 
experiments and interpolated the normal data. 



ReUtlTe Humidity 


Per Cent, of 
Mortality 


Melanism 


Arerage 


Bange 


Mode 


Range 


100 
95 
84 
74 
66 
60 
50 
34 


100-100 
82-100 
55-100 
43-100 
33-100 
30-100 
25-83 
10-55 


90 
30 
15 

r 

35 

80 
92 
99.6 


4 
7 

12 
9 

11 
5 
3 
2 


2-9 

3-11 

7-16 

6-lS 

6-18 

3-11 

1-7 

1-4 



It will be seen that mortality increases rapidly as the humidity 
departs from normal but this can not account for the change 
in color since the range of melanism is doubled and in three of 
the experiments even the mode falls below the normal range. As 
stated by the author: 

The results of experiments with deviations of humidity are almost 
exactly the same as those which were obtained from experiments with 
deviations of temperature. Such deviations from the normal either to- 
ward an increase or a decrease, produce up to a maximum increased 
pigmentation and a consequent melanic tendency, but beyond this the 
effect is reversed, pigmentation is retarded, and the tendency toward 
albinism becomes more and more pronounced as the deviation from the 
normal becomes greater. 



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No. 566] EDAPHOSAUBUS CBUCI6EB 126 

The point which concerns the present discussion is that not 
only does humidity have a definite regularly acting influence, but 
that its results are similar to those of temperature and, as with 
temperature, plus and minus variations of certain intensities 
bring about similar effects. If, as has usually happened, the hu- 
midity is not controlled in experimental work on the effect of 
temperature, how can it be said that the observed results are the 
effect of changes in temperature t 

Tower made certain experiments in which both temperature 
and humidity are abnormal, normal average temperature being 
taken as 22.2** C. Unfortunately, proof reading or something of 
the sort was faulty when it came to publication. Experiment 
26 would be the most valuable for our present purpose, but the 
table includes records of relative humidity 35 and 39 per cent, 
above normal, ». e,, relative humidities of 109 and 113 per cent., 
respectively, if, as in the other experiments, 74 per cent, is 
'* normal" humidity. These are clearly impossible. The text 
figure illustrating this experiment does not help us since hu- 
midities are not given and furthermore the temperatures in the 
figure are rather consistently one degree different from those 
given in the table. Since there are two errors in text-figure 15, 
which illustrates the experiments with humidity as the only vari- 
able, it is likely that the figure is the thing that is at fault here. 
Several other similar discrepancies could be pointed out (as, for 
example, the temperatures in experiment 24, which concerns the 
combination effect of humidity and temperature) but it is prob- 
able that the author's notebook records are correct and the tem- 
perature discrepancies in the published report are so slight that 
we may accept his conclusion. It is 

that when temperature and moisture are the variables in a given en- 
vironmental complex, the trend of general color modification is con- 
trolled by moisture (relative humidity), excepting in conditions where 
the temperature deviation is so excessive that the ordinary physiological 
and developmental processes are greatly inhibited. In experiments 
approximating natural environmental complexes, however, moisture is 
the dominant factor in influencing coloration. 

Even if there were no other reasons for urging the necessity 
of taking humidity into account, I feel that Tower's work would 
be ample justification. Before taking up those reasons let us 
notice several cases where, on account of the striking results of 
the experiments, we must regret our lack of information as to the 
real cause or the relation of the several causes. 



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126 THE AMERICAN NATURALIST [Vol. XLVm 

This same work of Tower is one of them. The effects just noted 
were merely ontogenetic. However, he made other experiments 
in which the effect seemed to be passed on by heredity. The fac- 
tors in the various experiments with L, decemlineata were 35^, 
45 per cent, and low atmosphere pressure (p. 287) ; **hot, dry" 
(p. 288) ; **hot, dry and low pressure'' (p. 288) ; and '*hot, 
moist'' (p. 291), probably 31.2°, 94 per cent. Those with L. 
mulitceniata were 30° and saturation (p. 292 and p. 293) ; and. 
the one with L, undecemlineata was * * 10 C. above the average and 
a relative humidity of 40 per cent.*' The work is of such im- 
portance because of its pioneer character that it would be un- 
gracious to complain too strongly, but the fact is that it is 
impossible to tell from the data given whether the effects are 
caused by humidity or by temperature or by a combination of 
the two. Bateson's idea that there are no effects to be explained 
need not concern us here. 

There is a long series of interesting papers starting in 1895 
by Fischer. As has already been mentioned, he finds that certain 
high temperature grades produce effects which are similar to 
those produced by certain low temperature grades. The con- 
ditions of humidity are rarely mentioned, not to say considered. 
However, he occasionally confesses that they are important, as 
when he tells us* that it is necessary to have the warm air dry and 
the cold air moist in order to get similar forms of Vanessa by the 
application of moderate cold and moderate heat. I suspect hu- 
midity largely enters into the other experiments also for in one 
with high temperature,** which gave the same results as certain 
low temperatures and presumably high humidity he says the hu- 
midity was high. 

Like Tower's experiments with beetles these concern color 
alone. Pictet* and Federley,'' especially, have considered the 
effect of environmental factors upon the form of lepidopterous 
scales. Federley calls his work ''Temperatur-experimente" and 
Pictet ** Influence de I'Humidite" but neither enables us to dif- 
ferentiate the effects of the two factors, although both obtained 
striking results. Kominsky® modified to a considerable extent 

^Algemeine Zeiischrift fur Eniomologie, VIII, p. 274, 1903. 

5 Illustrierte Zeiischrift fiir Eniomologie, IV, p. 134, 1899. 

^MSmoires de la SocUiS de Physique et d'Risioire Naturelle de Gen^e, 
XXXV, Fasc. 1, 1905. 

7 Festschrift fiir Palmen, No. 16, Helsingfors, 1905. 

8 Zool, JahrhUcher. Aht. fiir Allg, Zool. und Physiologic, pp. 321-338, 
1911. 



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No. 566] SHORTER ARTICLES AND DISCUSSION • 1 27 

not only the color and form of scales but also the form of an- 
tennae, legs and other body parts of Lepidoptera. He exposed 
the pupae to 42.5** C, humidity not given; 38° to 39° C. and 42* 
to 43° C, relative humidity 80; 8° C, "high humidity"; 0° C, 
''very high humidity"; —7.5 to 5° C, relative humidity 80-90 
and 50; and — 11** C, humidity not given. For the most part 
the humidity was high and probably had much to do with the 
results, but we can not be certain. 

All the experiments just considered were made upon pupae. 
It should be remembered that only about one fourth of the weight 
of lepidopterous pupae consists of solids, and that the only way 
they can replace fluids lost by evaporation is by chemical changes 
in these solids. It is probable that they do so to some extent, 
although this has not been accurately determined. It is known 
that under normal conditions pupae lose in weight and the per- 
centage of solids increases. Naturally, a change in the humidity 
of the surrounding air would modify this physiological process 
and it is difiScult to believe that it has not quite as much effect as 
changes in temperature, the humidity remaining the same. It 
is easy to see that, if the air is made more absorptive or less ab- 
sorptive either by the temperature changes themselves or by other 
means, and then the physiological activities are slowed or quick- 
ened by temperature changes, the effects will be much greater 
and might easily pass as due entirely to the temperature changes. 

The species which have wet and dry season forms in regions 
where the temperature is fairly constant throughout the year, as 
well as the tendency for the animals of moist regions to be mel- 
anic and of arid regions to be light colored, speak for the impor- 
tant influence of humidity. But there is another point in 
distribution to be considered. The study of distribution was 
long, and still is, largely an effort to get the ranges of animals 
and plants to fit isotherms. When yearly averages do not work, 
winter minima or summer maxima or accumulated temperatures 
are tried. The success which often attends these efforts shows 
that man is very ingenious and also that temperature is really 
one of the controlling factors, but it does not show that it is the 
only factor or, in fact, that it has any direct influence. 

The areas of grassland and forest in North America cut across 
isotherms as though they were merely political boundaries but 
Transeau* has shown that if we plot the ratio of temperature to 
• Ameb. Nat., XXXIX, pp. 875-889, 1905. 



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1 28 THE AMEBIC AN NATURALIST [Vol. XLVm 

humidity we get a very close corresjwndenee between distribution 
and climatic factors. Schimper^® has brought together a great 
deal of evidence which indicates that, as far as plants are con- 
cerned, even the major divisions of the world's surface into arctic, 
temperate and tropical are fundamentally a question of the de- 
mand for and supply of water. 

Furthermore, if recent climatic changes have an effect upon 
the origin of new characters and the distribution of the organisms 
possessing certain characters, humidity is deserving of more 
attention than temperature, since practically the only evidence 
we have of such changes concerns humidity. 

It should not be forgotten that even aquatic oi^anisms are 
subject to what amounts to changes in humidity. Peat bog plants 
take on many characteristics of a desert flora, although their 
roots are covered with water. It is water, however, which is 
not easily available, because of the chemicals which it carries. 
It is water which is physiologically dry. 

Finally, the great amount of work which has been done upon 
artificial parthenogenesis and related subjects is, in a way, a 
study of the influence of environmental factors. The obvious 
factors concerned have usually been various chemicals but at 
foundation humidity, in a broad sense, the addition or withdrawal 
of water by osmosis seems to be a factor of prime importance. 

Frank E. Lutz 
American Museum op Natural History 

10 "Plant Geography upon a PhTsiological Basis," translated by W. B. 
Fischer. Oxford, 1903. 



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FOR SALE 

ARCTIC, ICELAND and GREENLAND 

BIRDS' SKINS, 

Well Prepared Low Prices 

Particulars of 

G. DINESEN, Bird Collector 

Husavllc, North Iceland, Via Leidle, Ensrland 



WANTED TO PURCHASE 

a set of BIRDS OF AMERICA by J. J. Audubon. 
7 or 8 volumes, please report, stating cash price, stat- 
ing condition, binding and dates of volumes. 

P. C. HARRIS, 
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TO OOLOQISTS 

and ENTOnOLOGISTS 

W. F. H. ROSENBERG 

Importer of Ezotio Zoological Specimens 
57, Haverstock Hill, London, N* W., finglaad 

Begs to announce the publication of two new 
Price Lists : No. 18, Exotic Lepidoptera (over 8000 
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ALL MUSEUMS SHOULD 
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AJ] specimens sent on approval. 
Please state which lists are reqnired and give 
name of this periodical. 



FINE LAND 5HBLL5 

I have in stock and for sale nearly ten thousand spedet 
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cash. Correspondence solicited with travelers and explorers. 
Only the finest material handled. WALTER P. WEBB, 
202 Westminister Road, Rochester, N. T., U. S. A. 



The University of Chicago 

Offers instnictian durinf the Sum- 
mer Quarter on the same basis as 
during the other quartets of the 
academic year. 

The undosnuluate colleges, the 
graduate schooU, and the profes- 
sional schools provide courses in 
I ArtB, Htmvainrm, Scimnem, 
Commmrem and AaminiMtra' 
Hon, Law, Mmdieinm, Educa* 
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I is given by regular members of the 
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professors and instructcn from 
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Summer Quarter, 1914 
Itt Term June 15-Jnly 22 
2d Term July 23- Aug. 28 

Detailed announcements wiU be 
sent upon application. 

The University of Chicago 

Mitchell Tower Chicago, IlKnoia 



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The American Naturalist 

Ml ■■ t i W h h i J fai 1867, Dwrotod to iIm Ainmtmmm^ W lb* Pioloiicri 
SpMiid iUlMMM to tU FMton W OrcMie ErofartlM ana Hmdlly 



ooNTcmra op the Auourr number 

Geiwtioftl Stodiet on 0«iioUi«m. IV. Br. Bndlty 

HooreDATii, 
The Infloftne* of Protneted and Intermittent Fiftlnf 

upon Growth. Dr. 8en;iiii Morgnlli, 
dmbrien HolothnrUuM. Anttln H. Clerk* 
Shorter Artiolet end Diaeosiion: Vlebllity end Ooapr 

linginSrosophile, P.W. Whiting. TheBemilte 

Obteined'by erosiing wtm meii L. end Kochleene 

wexleene Bohred, Kery G. Leoy. 



OONTCMTB OF THC MPTCMBEII NUMBKR ^ 
VheNetnrel Hlftoryof the Nine-bended AxmediUe 
of Texea. rr o f im g H. H. Kewnum. 



Genetieel Stodiee onOenothere. 
H. DeTlB. 



IV. Dc Bredley 



Derwlniimlnl^Qreetrjr. Dr. Beiiheel Zoa. 

Noteeone Dtfferentlel Mortelitj ohferred bciiweeB 
TenebroebtenriiendT.siolitor. Dr. 
Gartner. 



CONTCNTS OP THC OCTOBCII NUMBCII 

▲ Ck>ntrlbntlon toweidi en AnelTeie ef the Ffoblem 
of Inbreeding. Dr. Beymond PeerL 

The Inheritenee of Ooet Color in Hotiei. P ro l tMor 
W.& AndeiKMU 

The Verietiont In the Nnaberof VertebnB end Ven* 
irel Sentte in Two Bneket of the Genoa Begine. 
Profenor Alezender G. ButhTen end Czyitel 
Thompaon. 

Shorter Artiolet end Beporta: The SImiilleBeona 
KodUicetion of Diatinet Mendellen Vecton: Pto- 
feaaorB.A.£meraon. TheFonithlntemetlooel 
Genetic Oonftoenee : Dr. Frenk M. Sorfeee. 



OONTKNTB OP THC NOVCMBCll NUMBCK 

The Blleet on the Oflipring of IntozleettBg the Mele 
Perent end the Tzenamlaaion of the Defeeta to 
Bobaegnent Gene m tiona. Dr.CherleaB.8toekeEd. 

Bnpplementery Stodlea on the DUEerentlel Moitalitgr 
with raapect to Seed Weight in theGfreifnetton 
of Gerden Beena, Dr. J. Arthur Herxla. 

Shorter Artlolea end Diaciiaaion : Bedpiooel Croaeea 
between Beeye'a Pheeaent end the CnButmw 
Bingneek Pheeaent prodndng Unlike Hybclde. 
JohaCPhUUpe. 



CONTCNTS OP THC DCCCMBCII NUBIBCII 

TheFittttonofCherectertnOrgeniama. ByBdweid 
Sinnott. 

Inheritenee of Left^hendedneaa. Ptef eiaor TnnoU 

Bemeley. 
Snpplementery Btndiea on the Diflerentiel MorteU^ 

with Beapect to Seed Weight in the Germlnetlon 

•f Gerden Beena. H. Dr. J. Arthur Herria. 
Shorter Artielea end Diacnaalon : A Croaa inyolTing 

FonrPeiraofHendelienChereeterainlliee. C 

C. Little, J. CPhOllpe. 
Index to Volume XLVn. 



OONTCNTB OP THC JANUARY NUMBER 
A Genetie Anelyaia of the Chengee predneed by 

Selection in Xzperimenta with Tobecco. Pro- 

feMor B. M. Beat end H. K. Heyea. 
Gynendromorphoiia Anta, deecribed daring the I>e> 

cede. 1906-1918. Piofeaeor WlUIem Mortoa 

Wheeler. 

Shorter Artielea end DiaeoMlon: On the Beenlte of 
Inbreeding e Mendellen Fopoletlon— A Cocree- 
tion end Bxtenaion of PreTlooa Ooneluaioiia. 
Dr. Beymond Feerl— laoletfon end Bdeetloii 
elUed in Principle. Dr. John T. Gnliek. 



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130 THE AMERICAN NATUBALIST [YouXLYUl 

In the pasty mucli of the work that has been done on 
zoogeography has dealt with a study of the facts of dis- 
tribution, both present and past, as they sta9d, together 
with a study of the factors influencing distribution and 
speculations regarding the explanation of somo of the 
interesting and apparently anomalous facts thus brought 
to light. In all of this work, the distribution of animals 
has been considered almost entirely as the effect of cer- 
tain biological and geological causes. The present paper 
is intended to show that the distribution of animals is not 
only the effect of other causes, but is in itself the cause 
of other effects, and that extent of distribution has a 
direct influence on the modification and speciation of the 
group concerned. 

To find out how far-reaching and how potent is this 
effect, much further study is necessary, not only of the 
distribution of various groups, but of their classification 
and systematic relationships as well. 

In brief, the effect of extent of distribution on groups 
of different systematic rank may be stated as foUows: 
As the range of a group of animals, be it genus, family, or 
order, is extended, the species increase out of proportion 
to the genera, the genera out of proportion to the families, 
and the families out of proportion to the orders. In 
other words, if we assume that in a distributional area 
of certain extent, there are three genera and six species, 
in a distributional area of twice that size, there will not 
be six genera and twelve species, but more probably only 
four or five genera, and twelve species ; i. e., if in the first 
case the index of modification (a term here used to indi- 
cate the average number of species per genus) be two, in 
the second case it will be greater than two. 

As new distributional areas are added, other factors 
remaining equal, there is a constant increase in number 
of species and subspecies, going hand in hand with a 
diminishing rate of increase in genera, the result being a 
constantly larger index of modification as the area in- 
habited by a group of animals is extended. 



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No. 567] EFFECT OF DISTRIBUTION ON SPECIATION 131 

It should be remarked that a unit of area in this con- 
nection should be considered a distributional unit, not a 
geographical unit. In other words, while the addition of 
one hundred square miles might or might not involve a 
change in the life of a region, the addition of a new ^^life 
zone,'* **fauna,'* or association" (see p. 155) would 
inevitably involve a biotic change, and therefore the addi- 
tion of one or several of any of these distributional areas 
should be considered as an addition of a unit, comparable 
to another unit of similar kind. 

Two possible ways of testing this hypothesis present 
themselves. "We may compare the faunas of distribu- 
tional areas of dissimilar size, or we may compare the 
specific and generic differentiation found within families 
occupying areas of different extent. The former method 
we should expect to work out with a fair degree of 
accuracy, but the latter involves so many modifying cir- 
cumstances that even if sufficient data were at hand, it 
would be difficult to prove anything by it. In the first 
place there is the difficulty of comparing, in a distribu- 
tional sense, the areas occupied by different families, 
since, as pointed out above, the geographic areas do not 
necessarily coincide at all with distributional areas; in 
the second place, while it is justifiable to compare the 
speciation of a family in one region with the speciation of 
the same family in another region, it is of doubtful value 
to compare the speciation of one family with that of 
another in the same or different regions, unless the other 
factors controlling their speciation be comparable or 
nearly so. In view of this there are few families which 
could be advantageously compared with each other as to 
speciation in relation to extent of distribution, yet in the 
families which do seem to lend themselves to such a com- 
parison, the evidence aU points towards the correctness 
of the law here proposed. 

The bats seem as favorable for such an interfamily 
comparison as any group of mammals that could be 
selected, and the table (Table I) of their distribution by 



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132 



TRE AMERICAN NATURALIST [Vol. XLVHl 



TABLE I 

Distribution and Spegiation of Families of Ghibopteba 

Data Derived from Sdater and Sclater (1899) 



Family 



Distribution 



Gen. 



I Index 
SP. I of Mod. 



Cosmopolitan 

Warm parts of both hemispheres . 



VespertilionidaB . 
Emballonuridffi . 

Ptoropodidae Old World, 

Rhinolophidae lOld World 

Nycteridse Warm parts of Old World 

Phyllostomidas ^ Neotropical 



17 
15 
18 
6 
2 
36 



190 
79 

110 
61 
15 
81 



11.18 
6.27 
6.11 

10.16 
7.60 
2.25 



families is significant. One family, the VespertilionidaB, 
is cosmopolitan, inhabiting every zoologic region and 
every life zone, and it has 11.18 species per genus, the 
highest of any family of bats. The Phyllostomidae, on the 
other hand, has the narrowest range, occupying only the 
warm zones of one zoologic region, namely, the neotropic, 
and has in 36 genera only 81 species, giving 2.25 as the 

TABLE n 

DlSTBIBUnON AND SPECIATION OF FAMILIES OF INSEGTIYOBA 

Data Derived from Sclater and Sclater (1899) 



Family 



Distribution 



Gen. 


8p. 


11 


126 


2 


16 


11 


25 


2 


15 


3 


17 


2 


3 


1 


2 


1 


7 


7 


21 . 


1 


2 ! 



Index 
of Mod. 



Soricidffi. 



Erinaceidffi . 



TalpidsB. 
TupaiidsB. 



. . . Palearctic, Ethiopian, Oriental and 

Nearctic resions, all zones | 11 

. . . Palearctic, Ethiopian, and Oriental 

regions 

. . . Palearctio and Nearctic regions, tem- 
perate zones only 

. . . Oriental region, warm zones 

MaoroscelidaB .Ethiopian region, warm zones 

Potamogalidffi I Central Africa and Madagascar, 

I tropical zones 

Galeopithecidffi {Malay only, forests, tropical zones. . . , 

Chrysochloridas .... !South Africa I 

Centetidffi Madagascar , 

Solenodontidas Cuba and Hayti | 



11.36 

8.00 

2.27 
7.60 
5.66 

1.50 
2.00 
7.00 
3.00 
2.00 



index of modification. The other figures in this table are 
significant, but the indices of modification in the families 
RhinolophidaB and Nycteridae are abnormally large, and 
will probably be reduced by subsequent subdivision of 
genera, or discovery of new forms. 
Table 11 shows the generic and specific differentiation 



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No. 567] EFFECT OF DISTRIBUTION ON SPECIATION 133 

of the various families of Insectivores, but as some of the 
families have not been as intensively studied as others, 
and as the conditions affecting their distribution and 
speciation are so different in different families, we could 
hardly expect accurate results, and yet the table clearly 
shows a tendency for the families having wider ranges 
to have a higher index of modification, the almost cosmo- 
politan shrews, for instance', having 11.36 species per 
genus, and the families with restricted range (Galeopi- 
thecidae, Solenodontidae, Centetidae and Potamogalidae), 
having only 1 to 3 species per genus. The Talpidae and 
Chrysochloridae do not seem to conform in their speciation 
to what should be expected. 

When the specific and generic subdivisions of all the 
families of mammals have been worked out more per- 
fectly, and their ranges in a distributional sense, i. e., 
through life zones, faunas, and associations, are more 
accurately known, some interesting facts concerning the 
relation between their indices of modification, and the 
extent of their ranges, might be brought out. 

It is interesting to note that there is a considerable 
number of conspicuous examples of wide-ranging genera 
which are remarkably poor in species. Among carnivo- 
rous mammals there are many such cases, these animals 
seeming to be adaptable to an almost unlimited range of 
environmental conditions without modification, or, in 
other words, their germ plasm, is not stimulated to change 
by altered conditions of climate or environment. The 
tiger, for instance, is equally at home in the bleak frozen 
stepi>es of Siberia, or in the hot humid jungles of India. 
The genus Cynaelurus is widely distributed over the 
Ethiopian and Oriental regions, and yet it contains but a 
single species, with several geographic races. Among 
birds there are a number of similar examples, the most 
striking case, perhaps, being Pandion, a cosmopolitan 
genus with but a single species. The same peculiar condi- 
tion occurs among lower animals, as for instance in the 
Dinoflagellate genus Diplopsalis, which is cosmopolitan 



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134 



THE AMERICAN NATUBALIST [Vol. XLVHI 



TABLE inj 

Speciation of Mammals in Various Distbibutional Areas in CSauvobnu 

Data from GrinneU {191$ A), (1908), Orinnell and Swarth (191S) 





Boreal aod Upper Trmnsltioo Zooee 


Group 


Sao Jae. Mts. 
(SSOSq.M.) 


San Bern. Mta. 
(MOSq.M.) 


Sierra Range 
(80,000 8q.ll.) 




OoD. ! 8p. 
1 1 


Gen. 8p. 


Gen. 


8p. 


Ungulata 


1 , 1 


2 

1 
1 

21 

6 

1 
7 
1 
1 
1 
1 
1 
2 

14 

2 
3 

7 

1 
1 

4 

2 

2 

4 
4 


4 


Bovids 


1 

7 

4 

2 

1 

6 

2 

1 
3 

2 

1 

1 

2 
2 


1 

8 

4 

3 

1 

6 

2 

1 
3 

2 

1 

1 

3 
3 


1 


Cervids 


1 

10 
6 

3 

1 
1 

2(7) 

(2) 

1(2) 

1 

(1) 

(1) 

2 

1 
1 

2 
2 


1 

12 
6 

6 

1 
1 

2(8) 

(2) 

1(2) 

1 

(1) 

(2) 

2 

1 
1 

3 
3 


3 


Antilocapridffi 

Rodentia 


67 


Sdurids 


22 






Aplodontids 

Murids 


1 
17 


Geomyids 


5 


Heteromyidtt 

24apodida 


2 
2 


Ereihisontids 

Oohotonida 

Leporids 


1 
3 
4 


Camivora 


21 


FelidflB 


3 


Canida 


6 


Muatelidffi 


10 


Prooyonidffi 

Uraids 


1 
1 


Inaeotivora 

SoriddflB 


11 

7 


Talpids 


4 


Cheiroptera 

Phylloetomids 

Vespertilionids 

Moloeaids 


7 
7 






Total 


18 


20 


17(22) 


20(26) 


45 ; 100 






Indioes of modifioa- 
tion 


1.11 


1.17 (1.81) 


2.22 



in warm and temperate seas^ and yet is composed of not 
more than two species. No adequate explanation of these 
exceptional cases has been offered, and it is probable that 
their speciation, or lack of it, is due to conditions of their 
existence or constitution which we do not understand, or 
do not recognize. 



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No. 667] EFFECT OF DISTBIBUTION ON 8PECIATI0N 135 

To test the law by comparison of faunas of areas of 
different extent, a series of tabular comparisons of the 
faunas of various regions of different size and character 
was made. In all of these tabulations, care has been taken 
in the choice of areas for comparison to make them of un- 
equal size from a distributional point of view, and to 
make them reasonably comparable. An arctic and a 
tropical region, for example, are not considered reason- 
ably comparable as regards number of genera and 
species, nor is a region on the outskirts of the range of a 
group considered comparable with a region near its 
center of distribution. 

Table m shows a comparison of the mammals of vari- 
ous parts of California. The regions compared are as 
follows: (A) the boreal and transition zones of (a) the 
San Jacinto Mountain range, (b) the San Bernardino 
Mountain range, and (c) the entire Sierra range, includ- 
ing the Warner and Shasta Mountains to the north, and 
the San Bemardinos and San Jacintos to the south; (B) 
a comparison of all the zones of (a) the San Jacinto 
Mountains with the immediately adjoining country, (&) 
the Sierra range as defined above, and including their 
foothills, and (c) the entire state. 

A careful study of Table III brings out a number of 
interesting and significant facts, and bears out the law 
here proposed with unexpected accuracy, barring one 
seeming exception which, as we shall see later, can not 
truly be considered as such. 

Let us compare first the three areas in which only the 
two uppermost life zones are involved, and from which 
the species invading only the lower Transition zone have 
also been excluded. First, a word as to the areas com- 
pared. The Boreal and Transition zones of the Sierras 
take in over one half of all the representation of these 
zones within the whole state. These zones of the San 
Bernardino and San Jacinto mountain masses are, as 
compared with the entire range, very small indeed, and 
comprise almost as small areas as could justifiably be 



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t36 



THE AMERICAN NATURALIST [Vol. XLVIH 



TABLE niB 

(Data as above) 
(Data as in Table III A) 



Group 



Ungulata 

BovidsB 

Cervida 

Antilooaprids 

Rodentia 

Sduridffi 

Castorids. 

Aplodontids 

Morids 

Geomyids 

Heteromyids 

Zspodids 

Erethiiontida 

Oohotonids 

Leporida 

Carnivora 

FeGda 

Canida 

Must^da 

Prooyonida 

yrsida 

InBeotivora 

Soridda 

Talpida 

Cheiroptera 

Ph3^o«tomida 

VeepertUionida 

MoloKida 

Total 

Indices of modifi' 
eation. 



All Zoom 



San Jm. Mts. 

(2,600 Sq.M.) 



Gen. 



16 
6 



Sp. 



41 
7 



14 

4 

12 



4 
10 

2 

4 



Sierra Range 
(60,000 Sq.M.) 



Geo. 



28 

7 

1 
10 

1 
4 
1 
1 
1 
2 

16 

2 
3 

7 
2 
1 



Sp. 



110 

26 

1 

38 

9 

24 

2 

1 

3 

11 

20 

3 
9 
13 
3 
1 

12 

8 

4 

12 



11 
1 



California 
(158,000 Sq.M.) 



Geo. 



1 
2 

1 

31 

7 

1 

1 

11 

1 

4 
1 
1 
1 
3 

17 

2 
3 
9 
2 

1 



4 
2 

11 

1 
8 
2 



10 



41 

2 

2 

64 

19 

48 

5 

1 

3 

18 

51 

6 
17 

22 

4 
2 

20 

14 
6 

26 

1 
21 

4 



34 



68 



170 



68 



810 



1.85 



2.03 



4.56 



considered to be individual f annal nnits. The San Jacin- 
tos are somewhat smaller than the San Bemardinos, bnt 
the difference is almost inconsiderable when compared 
with the Sierras. Before examining the table, let us see 



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Na 567] EFFECT OF DISTRIBUTION ON SPECIATION 1 37 

what conditions in number of genera and species wonld 
be expected in these three areas. The San Bemardinos, 
being almost as small a fannal unit as should be sepa- 
rately considered, we should ezi)ect to approach a mini- 
mum index of modification^ i. e., a minimum number of 
species per genus, approaching one as a limit. On the 
San Jacintos, these being smaller than the San Bemardi- 
nos, we shotdd expect fewer types according to the law 
suggested by Grinnell and Swarth (1913), that the num- 
ber of persistent types in a disconnected area varies 
directly with the size of the area. On the entire Sierra 
range we should expect, due to the greatly increased 
territory, a considerable increase in genera, but a very 
much greater increase in species. Looking now at Table 
m, we find that with the single exception of the car- 
nivores on the San Bernardino Mountains, not one dis- 
crepancy exists. The Ungulates, Insectivores and bats 
are represented by the same numbers of genera and 
species on both of the small areas, and all of them show 
a marked increase in genera and species on the larger 
area, in every case with an increase in the index of 
modification. 

The rodents, which show a larger degree of differentia- 
tion than any of the other groups, show a very interesting 
advance in the index of modification as the area is ex- 
tended. The carnivores, as stated above, show a seeming 
discrepancy, inasmuch as there are six genera and six 
species existing on the San Jacintos, and only two genera 
and two species on the San Bemardinos, whereas, if they 
conformed with our laws of distribution, we should expect 
at least six, and possibly seven or eight, species to be 
found there. On page 35 of Grinnell 's ** Biota of the San 
Bernardino Mountains'' (1908) we find reference to a 
number of carnivores now rare or extinct on the San 
Bemardinos, which undoubtedly have been exterminated 
by man within the last fifty years. Counting these forms, 
which it seems to me we are justified in doing, the table 
bears out the law without a single exception, not only for 



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138 



THE AMERICAN NATURALIST [Vol. XLVIII 



the total of mammalian forms, but the totals for each 
order and for each family. 

In comparing the three areas in which all the life zones 
are involved, the truth of the effect of extended distribu- 
tion on speciation is still more forcibly impressed upon 
us. In this case we are comparing areas which are suc- 
cessively larger in size, the San Jacintos, with their foot- 
hills and low passes involving the fauna of an area of 
about 2,500 square miles, the Sierras, about 60,000 square 
miles, and the whole state of California about 158,000 
square miles. The following table, derived from Table 
III, is very significant in showing the diminishing in- 





Genera 


Species 


Index of ModificaUon 


Group 


SanJac. 


Sier. 


CaL 


8anJao.{ Sier. 


Gal. 


SanJao. 


Sier. 


Cal. 


Unsulates 

Rodents 

Carnivores 

Insectivores... 
Cheiroptera. .. 


2 

16 

9 

3 

4 


3 

28 

15 

5 

7 


4 
31 
17 

6 
11 


2 
41 
10 

3 

7 


7 

110 

29 

12 

12 


10 
203 
51 
20 
26 


1.00 
2.56 
1.11 
1.00 

yr5 

1.85 


2.33 
3.93 
1.93 
2.40 
1.71 


2,60 
6.45 
3.00 
3.33 
2.36 


Totals 


34 


58 


68 


63 


170 


310 


2.93 1 4.56 



crease of genera, and the constantly increasing addition 
of species as the area is enlarged. 

By comparing the upper zones of the San Jacintos 
with the San Jacintos as a whole, and the upper zones of 
the Sierras with the Sierras as a whole (see Table HI), 
we find that increasing the life zones has in a lesser 
degree the same effect as increasing the geographic area 
regardless of zones; in other words, adding life zones 
tends to have the same effect on speciation as adding 
faunas and associations without life zones. The follow- 
ing table (derived from Table HI) illustrates this: 



Mammal! 


San Jac. 
(Upper Zonae) 


San Jac. 
(All Zonae) 


Sierras 
(Upper Zones) 


Sierras 
(All Zones) 


Genera 


18 
20 
1.11 


34 
63 

1.85 


45 
100 
2.22 


58 


Species 


170 


Index of mod 


2.93 



Another rough test of the hypothesis was made in a 
comparison of the mammalian faunas of some of our 



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No. 667] EFFECT OF DISTRIBUTION ON SPECIATION 139 

large continental islands and zoologic regions^ the results 
being shown in Table IV. The data used in this table are 

TABLE IV 
Spichation of Mammals in Yarious Continental Islands and Zoolooio 

Begions 
Daia from Solater and Sclater (1899) 



Group 


AfHca 


AuttnUUn 
Region 


Austrftli* 


N«w 

Gnine* 


MadaffMOAr 
(228,000 Bq.M.) 




8p. 


Qen. 


Sp. 


Qen. 


8p. 


Gen. 


8p. 


Gen. 


Sp. 


Gen. 


tJngulatfls. . . 

Rodents 

Caniivores... 
InBoctivores.. 

Bats 

Lemurs 

Primates 

Hyraces 

Elephants. .. 
Edentates... 
Marsupials . . 
Monotremes. 


156 

196 

59 

73 

101 

8 

72 

14 

1 

6 


35 

41 
22 

8 

19 

3 

6 

1 
1 
2 


69 
83 

144 
5 


8 
26 

36 
3 






18 
39 

36 
3 


5 
16 

14 
2 


1 
13 

9 
20 
21 
36 


1 
7 
7 
9 
12 
11 


Totals 


685 


128 


301 


73 


169 


59 


96 


87 


100 


47 


Index of mod- 
ification. . . 


5.35 


4.12 


2.86 


2.59 


2. 


13 



by no means up to date, being taken from the summaries 
in Sclater and Sclater (1899), but the subsequent additions 
to the faunas of the places concerned, and the splitting 
up of genera and species, have probably been approxi- 
mately proportionate in each of the five areas, and there- 
fore the figures used are sufficiently accurate to be signifi- 
cant Comparing Africa, the Australian region, Australia, 
New Guinea and Madagascar, which rank in size in the 
order given, we find that the indices of modification of 
their mammalian faunas are as follows: Africa 5.35, 
Australian region 4.12, Australia 2.86, New Guinea 
2.59, and Madagascar 2.13. Certainly these figures are 
significant. 

Comparing the mammalian faunas of the various 
islands of the Philippine Archipelago (Table V), we find 
that there is even here some corroboration of our law of 



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140 



THE AMERICAN NATURALIST [Vol. XLVIII 



TABLE V 

Speoation of Mammals in Islands of thb Philippink Abohipelago 

Data from Holliaier {1912) 



Island 



Sq. Miles 



Sp. 


Gen. 


72 


40 


61 


32 


16 


13 


14 


13 


10 


8 


21 


18 


17 


11 


9 


8 


8 


7 


3 


3 


5 


4 



Index of Mod. 



Luson .... 
Mindanao . 
Samar. . . . 
Negros. . . . 
Panay .... 
Palawan. . 
Mindoro. . 

Leyte 

Cebu 

Bohol 

Masbate. . 



40.969 
36.292 
5,031 
4,881 
4,611 
4.027 
3.851 
2,722 
1,762 
1,441 
1.236 



1.80 
1.90 
1.23 
1.07 
1.26 
1.16 
1.54 
1.12 
1.14 
1.00 
1.25 



speciation. Considering the large element of chance in 
the animal population of a group of islands of such small 
size as those of the Philippines, where the various islets 
are at a varying distance from each other, and their 
faunas have originated from diflFerent sources, the rela- 
tion between their size and the differentiation of their 
forms is remarkably regular. In Table V, where the main 
islands have been listed in order of size, with their num- 
bers of genera and species of mammals, the deer have 
been excluded entirely, since their generic and specific 
differentiation is in too chaotic a state to be used. The 
most striking fact brought out by the table is the lead 
which the two large islands, Luzon and Mindanao, show, 
not only in total number of forms, but in index of modifi- 
cation as well. With the possible exception of Mindoro 
and Palawan, practically none of the smaller islands is 
supporting as large a variety of mammalian forms as 
could be expected of it, a fact which might be explained 
in a number of ways. 

In all of the tabulations given, the marine mammals 
have been entirely excluded since the factors affecting 
their distribution and speciation are so different from 
those of terrestrial mammals. In the majority of cases 
marine mammalian families have a paucity both of genera 
and species, a circumstance brought about by a number 
of factors. Generally speaking, large, wide-ranging 



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No. 567] EFFECT OF DISTRIBUTION ON SPECIATION 141 

forms, or forms which are poor in nmnbers of individ- 
nalsy are poor in genera and species, possibly due to the 
comparative uniformity of their environment, which is 
usually coincident. Most marine mammals are of these 
kinds, and their paucity of types is emphasized by the 
comparative uniformity of their environment, even in the 
most widespread groups. From a distributional point of 
view, i. e., taking into account life zones, faunas and 
associations, a cosmopolitan, oceanic, surface group of 
animals does not range through as great a variety of 
ecologic niches and environmental and climatic condi- 
tions as does a cosmopolitan terrestrial group. 

In order to determine whether the principles of distri- 
bution and differentiation here set forth would apply to 
birds as well as to mammals, a number of series of com- 
parisons was made as with mammals, and with exactly 
comparable results. 

TABLE VI 

SpsaATioN OF Birds in Various California Arbas 

Data from GrinneU (19133), {1908), WiUett (191g) 



Group 


8*11 Bernardino Mts. 
(2,000 Sq.M.) 


Southern Californi* 
(«0,000,8q. M.) 


California 
(158.000 8q.M.) 




Gen. 


8p. 


Gen. 


Sp. 


Gen. 


Sp. 


Pluseres 


62 

16 

8 

5 

1 
1 
3 
1 
2 
2 
1 


82 

20 

3 

5 

1 
1 
3 
1 
2 
2 
1 


79 

19 
7 

10 
2 
3 
4 
5 
7 
5 

12 


114 

23 

7 

14 

2 

3 

4 

6 

7 

5 

14 


87 

20 

8 

12 

3 

6 

9 

6 

8 

11 

16 


197 


PiearuD 


38 


Striges 


15 


Aecqiitres 


17 


CohimbflB. 


3 


<Vlli 


11 




10 


Grues 


8 


Waden 


11 


Anseres 


11 


other water birds... 


26 


Total 


97 


121 


163 


199 


186 


347 






Index of mod 


1.: 


25 


1.30 


1.87 



Table VI gives a comparison of genera and species 
of resident birds of (a) the San Bernardino Mountain 
region, (&) Southern California, and (c) California as 
a whole. Almost without exception, in each individual 
group of birds there is a reduction in the index of modi- 



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142 



THE AMERICAN NATURALIST [Vol. XLYIH 



fication as the area is restricted from Califomia to the 
Pacific Coast region of Southern California, and finally 
to the San Bernardino region. The totals reflect the trend 
in each gronp. While in the largest area the nnmber of 
genera is considerably less than double what it is in the 
smallest, the number of species is mpre nearly tripled. 
The Southern Califomia area is intermediate. 

TABLE vn 

Speciation of Besidint Birds in Australll and Tasmania 

Data from North {1901-1909) 



Group 


AostnOia 
(2,947,000 Sq.M.) 


Tasmania 
(26.000 8q.M.) 




Sp. 


0«n. 


Fam. 


Sp. 


0«]i. 


Fam. 


Passeres • 


804 

29 

9 

27 

67 


119 

18 

2 

17 

14 


26 
6 
2 
2 
3 


68 

7 
1 

11 
11 


42 

7 
1 
9 
9 


16 


PfoaiuD 


3 


Striges 


1 


Acoipitres 


2 


Paittaoi 


3 






Total 


426 


170 


39 


83 


68 


24 


Index of cenerio mod 




4.36 




2.83 






Index of speoifio mod. 


2.30 




1.22 





Table VII shows a comparison of the families, genera, 
and species of resident birds of Australia and Tasmania, 
from North (1901-1909), Here again, in addition to a 
very marked diminution of the total number of types in 
Tasmania as compared with Australia, each group shows 
a considerable decrease in the ratio of genera to families, 
namely, from 4.35 in Australia to 2.83 in Tasmania, and 
of species, to genera going from 2.30 in Australia to 1.22 
in Tasmania. 

Table VlJJL is a similar comparison of (a) the resident 
birds of Ireland, from Hartert (1912), (6) the resident 
birds of all the British Isles, from Hartert (1912), (c) all 
the species of the Palaearctic region, the great majority 
of which are resident in one part or another, from Dresser 
(1902), (d) all the species of Japan, many of which are 
not resident, from Ogawa (1908), and (e) all the species 
of Kamtschatka, where the majority are resident, from 



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No. 667] EFFECT OF DISTRIBUTION ON SPECIATION 143 

TABLE Vni 

I^KSATioN OF Birds in Yabious Paleabgtio Begions 

Data from Hartert (191g), Dresser (190S), Oganoa (1908) and 

Stejneger (1885) 



Group 


Ireland 

(82,688 
8q/M.) 


Britiih 
IslM 


Palearotio 

Beffion 
(19,160,000 
Bq. m!) 


Japan 


Kam- 
taohatka 
(106,000 
Sq.k) 




Sp. 


Oen. 


Sp. 


Gen. 


Sp. 


Oen. 


8p. 


Gen. 


8p. 


Gen. 


Paflmran 


67 

4 
2 
7 
4 
4 

10 
4 
1 
8 

23 


35 

4 
2 
4 
2 
4 
9 
4 
1 
8 
14 


86 

7 

6 
12- 

4 

8 
16 

6 

1 

16 
30 


42 
7 
4 
7 
2 
7 

11 
6 
1 

12 

16 


610 
81 
34 
66 
29 
76 
97 
34 
31 
64 

129 


116 
21 
11 
21 
6 
19 
32 
13 
12 
24 
36 


180 
34 
14 
23 
12 
11 
46 
27 
23 
89 
83 


64 

16 

8 

14 

21 

12 
21 
28 


66 

8 
4 

16 

6 

26 
1 


28 

32 


38 


PicaruB 


5 


Strises 


3 


Aodpitres 


7 


Cdnmbte 





OfJli 


3 


T.fmi<^1^ ..... 


17 


Gmes 


1 


Waders 





Animrm 


20 


Other water birds 


18 


Total 


124 


87 


188 


113 


1,261 


310 


491 


204 


183 


112 






Index of mod. ......... 


1.42 


l.AA 


4.nn 


2.41) 


l.ftS 

























Stejneger (1885). The increase in index of modification 
from Lreland to the British Isles^ and then to the entire 
Palaearctic region, is almost exactly what should be ex- 
pected. The greater number of both genera and species 
in Japan as compared with Kamtschatka reflects the 
greater variety of ecologic niches in a warm country as 
compared with a cold one of comparable size. A com- 
parison of the resident species of Japan with the resident 
si)ecies of the British Isles would be of very great inter- 
est, but such a list of Japanese birds is not available. The 
very striking similarity between the speciation of birds in 
Kamtschatka, and that in the British Isles, both in num- 
ber of genera and of species, is very remarkable. The 
interesting manner in which the balance of nature is pre- 
served is shown by the large representation of raptorial 
birds to parallel the abundance of shore birds and Anseres. 
That reptiles and amphibians are influenced in their 
speciation by tiieir (iistribution is indicated by Table IX, 
which shows a comparison of the genera and species of 
amphibians, lizards, and snakes, in three of the geo* 
graphic areas defined by Cope (1898). 



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144 



TRE AMERICAN NATUBALIST [Vol. XLVUl 



TABLE IX 

Spegiation of Amphibia and Bsptilia in Nobth Amebicah Absas 

Data from Cope (1889), (1898} 



Group 


Lower Californim District 
(12,000 Sq.M.) 


Wettern Sab-region 
(600,000 Sq. M^) 


Medioolnmblan Begiea 
(4.600.000 Sq.lE) 


8p. 


Gen. 


Index of 
Mod. 


8p. 


Gen. 


Index of 
Mod. 


Sp. 


Gen. 


Index of 
Mod. 


Amphibia 

Lacertilis 

Ophidia 


4 
17 
16 


8 
13 
12 


1^ 
1.30 
1.33 


23 
28 
20 


10 

13 

9 


2.30 
2.15 
2.22 


130 
143 
191 


28 
31 
46 


4.64 
4.61 
4.24 



The ** Lower California district'^ consists of only the 
tip of Lower California; the ** Western subregion^' em- 
braces the Pacific slope of North America from Northern 
Mexico, east of the Sierras, to Oregon, where it crosses 
the Sierras to the Bocky Mountains, including northern 
Idaho, eastern Montana, and most of British Columbia. 
The **Medicolumbian region'^ includes northern and cen- 
tral Mexico, and most of the United States and Canada 
north to a line drawn diagonally from New England to 
Alaska, interdigitating on its border with the **Holarctic 
region. '* 

The almost exactly parallel increase in the indices of 
modification in the three groups of cold-blooded verte- 
brates considered, as the area is extended, is quite remark- 
able. All three groups average from 1.25 to 1.33 species 
per genus in the smallest area, from 2.15 to 2.30 in the 
intermediate area, and from 4.24 to 4.64 in the largest 
area. 

As suggested by Professor Kofoid, a factor influencing 
speciation in such diverse vertebrates as mammals, birds, 
reptiles, and amphibians, should be very widely appli- 
cable to speciation in the entire animal kingdom. 

A series of statistics relating to various orders of in- 
sects and other invertebrates has been compiled to ascer- 
tain whether in these groups as well as in vertebrates, the 
number of species increases out of proportion to the 
genera, as the size of the area, in a distributional sense, 
is enlarged. 



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No. 507] EFFECT OF DI8TBIBUTI0N ON 8PECIAT10N 146 



TABLE X 

Spsciation of "ELAmiDM IN Yabious Abbas of XJNBQUiii Sub 

Data from Sohwan (1906) 



RefloD 



Sq.MUes 



Sp. 


6«D. 


674 


66 


246 


36 


438 


63 


160 


40 


177 


41 


126 


36 


96 


28 


386 


42 


61 


20 


137 


24 


13 


7 



Index of Hod. 



Africa. 



India 

Borneo. . 
Sumatra. 

Java 

Oylon. . . 



Australia 

New Guinea. . 
New Zealand. 
Tasmania. . . . 



11,770,000 
228,000 

1.760,000 

296,700 

184.000 

60,000 

26.338 

2.947,000 

312,000 

104,760 

26,000 



10.43 
6.80 

8.26 
3.76 
4.31 
3.37 
3.42 

9.19 
3.06 
5.70 
1.86 



Table X was compUed to show the number of genera 
and species of beetles of the family ElateridsB in various 
continents and islands, the regions chosen for comparison 
being well defined areas of unequal size. 

A careful inspection of this table shows that with only- 
two exceptions the indices of modification are directly 
proportional to the size of the areas. Borneo and New 
Guinea, however, not only show a smaller index of modi- 
fication than should be expected of them, but are poor in 
total number of types. Nevertheless, when we reflect that 
these two islands are not nearly so thoroughly known to 
science as are the other areas considered in the table, no 
great significance can be attached to their seeming paucity 
of known types. 

Table XI shows tiie number of genera and species of 
Limnophilidse, a family of Trichoptera, in eastern North 
America (east of the Bockies) as compared with North 
America as a whole. It will be noticed that while in the 

TABLE XI 
SPldATION OF LnCNOPHILIDil (TBICHOPTBU) IN NOETH AlCESIOA 

Data from Ulmer (1907) 



Bagton 


8q. MilM 


8p. 


0«n. 


Index of Mod. 


North America 


8,000.000 
6,000,000 


98 
46 


27 
20 


3.63 


Eastern North Ameriea 


2.26 



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146 



TKE AMEBIC AN NATURALIST [Vol. XLVIII 



larger area the number of species is more than double 
what it is in the smaller area, the increase in genera is 
only about one third, increasing the index of modification 
from 2.25 to 3.63. 

Table XTT shows practically the same thing in the case 
of the hawk moths of the family Sphingidae. 



TABLE XII 

Speciation of Sphinqidji in Amebioan and African Abkas 

Data from de Rothschild and Jordan (1907) 



Area 



Sq. MilM 



Gen. Index of Mod. 



West Indies 

Mexico and Central America 

South America 

Mex., Cent. Am., and S. Am 

Mex., Cent. Am.. S. Am., and W. I. 

Bourbon 

Madagascar 

Africa 

Africa and Mad 

Africa, Mad., and Bourbon 



76,000 

976,200 

7.000,000 

7.975,200 

8,051,200 

965 

228,000 

11,772.000 

12.000.000 

12,000,965 



61 


20 


122 


34 


197 


35 


237 


40 


262 


41 


7 


5 


39 


20 


166 


48 


195 


53 


197 


53 



3.05 
3.58 
5.62 
5.92 
6.39 

1.40 
1.95 
3.45 
3.67 
3.71 



In this case two series of tabulations were made, one 
showing the number of genera and species in various 
Neotropical areas, and combinations of these areas, the 
other showing a similar tabulation for various Ethiopian 
areas, with similar combinations. It will be observed that 
the speciation in the West Indies is very large for the size 
of the area involved, but when we consider the abundant 
opportunity that has been given for isolation to operate, 
this is not surprising. The index of modification is quite 
low. Mexico and Central America have a larger specia- 
tion, compared with South America, than would normally 
be expected, the reason being that Central America is the 
American center of distribution. The index of modifica- 
tion, however, reflects the smaller size of the area, being 
considerably lower than that for South America. The in- 
crease in index of modification from 5.62 to 6.39, as areas 
are successively added to South America, is significant. 
Looking now at the Ethiopian regions, we find that there 
is the same disproportionate increase of species over 



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No. 567] EFFECT OF DISTRIBUTION ON SPECIATION 147 

genera in successively larger area6, the index of modifica- 
tion increasing from 1.40 in the small island of Bourbon 
to 1.95 in Madagascar, and 3.45 in Africa. Combining 
Africa and Madagascar, this is increased to 3.67, and with 
the island of Bourbon, to 3.71. 
Table AIJJL is one of especial interest, since it deals 

TABLE XIII 

SPECIATION OF MABINE GAMMABIDIA (AMPHIPODA) IN VaBIOUS SBAS 

Data from Stebhing (1906) 



Aras 


8p. 


G«ii. 


Index of Mod. 


Medit4¥TTAneftn 8«a 


147 
311 
476 
65 
588 
645 
735 
1,333 


67 
140 
176 

44 
101 
207 
214 
313 


2.19 


Arotio Ocean ^ . 


2.22 


N, Atlfrntri« Oc«ftn 


2.70 


S. Atlantic Ocean 


1.47 


Arctic and N. Atlantic 


3.07 


Arctic, N. Atlantic, and S. Atlantic 


3.11 


Arctic, N. Atlantic S. Atiantio and Med. Sea 

Whole family 


3.43 
4.22 



with a marine instead of a terrestrial group. It embodies 
the results of a compilation of the marine genera and 
species of Amphipoda of the suborder Gammaridea in a 
number of the oceans and seas of the world. Since it is 
primarily a cold-loving group, the largest numbers are 
found in the cold seas, the Arctic and North Atlantic being 
the home of considerably over half of the known marine 
si)ecies. It is very likely that when the Antarctic regions 
have been studied as thoroughly as the northern regions, 
the number of species from tiiat part of the world will be 
very considerably increased. At the time of Stebbing's 
work on Amphii)oda, our knowledge of Antarctic and 
contiguous areas was very meager. 

The steady increase of the index of modification from 
the smaller to the larger seas is striking. The Mediter- 
ranean Sea, although it is the most thoroughly known of 
all, has the lowest index of modification, namely 2.19, the 
Arctic Ocean comes next with 2.22, and then the North 
Atlantic with 2.70. The small number of species from the 
South Atlantic and Antarctic regions has already been 



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1 48 TEE AMERICAN NATURALIST [Vol. XLVIII 

mentioned, and its low index of modification may be at- 
tributed to the same sort of imperfect knowledge as in the 
case of Borneo and New Guinea in Table X. The con- 
stant growth of the number of species per genus from 
2.22 to 3.43 as the various seas and oceans are added to- 
gether, exactly parallels the results obtained in a similar 
way for a terrestrial group in Table XII. The comparison 
of the speciation of the largest area for which it was 
worked out, with the speciation of the entire group, many 
species and genera of which inhabit fresh water, is inter- 
esting, jumping as it does from 3.43 to 4.22. From the 
facts brought to light by this table it can hardly be doubted 
that practically the same influence is brought to bear on 
the speciation of marine as on terrestrial organisms by 
the extent of their distribution. 

The theoretical explanation here proposed for this phe- 
nomenon involves a number of complex problems relating 
to evolution and speciation, including isolation, effect of 
time, causes of specific and generic modification, etc., each 
of which will be dealt with in the following pages as they 
seem to influence the law here proposed. 

Let us first consider the factor of isolation in relation 
to the production of new forms. As excellently stated by 
Cook (1909), isolation can not be considered as a cause or 
factor in evolution, since changes in the characters of 
species are not dependent upon the subdivision of species 
to form additional species. To quote from him : 

The separation of species into two or more parts allows the parts 
to become different, but there is every reason to believe that evolutionary 
changes of the same kind would take place if the species were not 
divided. That the isolated groups become different, does not indicate 
that isolation assists in the process of change. It gives the contrary 
indication that changes are restricted by isolation. If isolation did not 
confine the new characters to the group in which they arise, the groups 
would remain alike, instead of becoming different. . . . Isolation is 
the shears that splits the species, not the loom that weaves it. 

Therefore, while isolation can not be considered a factor 
in evolution, it is an important factor in speciation. 
Species vary in many directions or orthogenetically pro- 



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No. 567] EFFECT OF DISTBIBUTION ON SPECIATION 149 

gress in a definite direction, but the trend of variation or 
progression may be different in one locality, and tend 
towards a different result, from that of another locality. 
Whether the evolution, usually in more or less divergent 
directions, of segregated groups of individuals be looked 
upon (1) as the accumulation of numerous slight varia- 
tions which have a different average character in any two 
portions of a species, as originally explained by Darwin 
(1859, Chap, 4) or (2) purely as the result of natural selec- 
tion, as argued by Wallace (1858), or (3) as the result of 
a change in the average character of two portions due to 
the imeven occurrence of mutations in the two portions, 
a conclusion reached by Dewar and Finn (1909, p. 380), or 
(4) as the result of orthogenetic evolutionary tendencies 
inherent in the species and influenced by the environment, 
as Eimer suggested (1897, Chap. 1), does not concern us 
here, — ^the general tendency appears to be that two iso- 
lated portions of a species as a general rule trend in 
different directions, and diverge farther and farther as 
long as they are isolated. 

It is assumed that the greater the length of time given 
for the influence of isolation to be felt, the farther apart 
are the two originally identical divisions likely to trend, 
however the dissimilar evolution be interpreted. As 
stated by Tower (1906), in speaking of the method of 
evolution of the CShrysomelid genus Leptinotarsa, 

We can interpret the conditions found by any of the current 
hypotheses; but explaining a condition by an hypothesis is not the 
same as that the conditions found are evidence in support of an 
hypothesis, although it is often so used. 

The existence of distinct variations, subspecies, and 
ultimately species and genera, in isolated areas is a too 
frequently observed phenomenon to be looked upon as 
anything else than a self-evident truth, but that this should 
necessarily be considered as supporting any particular 
theory of evolution can not be argued. 

The profound results of prolonged isolation may be 
observed in the fauna of some of our long-separated con- 



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150 THE AMERICAN NATURALIST [VouXLVIH 

tinental islands, such as Madagascar, Australia and New 
Zealand. Decreasing degrees of isolation may be observed 
in our West Indian islands, where some generic differenti- 
ation has occurred ; in the Santa Barbara islands, where 
there has been a differentiation of species; and the de- 
tached mountain ranges of Southern California, where the 
upper life zones are at present in an isolated condition, 
but have been so only long enough to develop a few new 
subspecies, and to lose many of the types of the mother 
range, in accordance with the law proposed by Grinnell 
and Swarth (1913) that **the smaller the disconnected 
area of a given zone, or distributional area of any other 
rank, the fewer the types which are persistent therein." 

From this it is apparent that the time element, in con- 
junction with isolation, may have a very decided effect on 
the number of genera and species in a family, but since, 
from a geologic point of view, animals appear to have 
reached a new equilibrium very quickly after a geographic 
change, the time element may have little effect on the num- 
bers of genera and species relative to each other in any 
given area. In other words, as fast as new genera are 
produced in a given area, the species within the genera 
will tend to be produced in the same ratio, thus leaving 
the index of modification unaffected. 

As an example of the effect of time and isolation let us 
take a hypothetical case. Let us assume that a certain 
island became divided into two islands of unequal size, 
and that after a short period of segregation, just long 
enough for the fauna to readjust itself to the smaller 
areas and reach a new equilibrium, we had say six species 
in three genera on the larger island, and three of the same 
species in two of the genera on the smaller one. After 
a long period of isolation we should have approximately 
the same number of genera and species on the two islands, 
but they would have diverged to generic differentiation. 
In other words, the effect of time in conjunction with iso- 
lation is to increase the number of genera and species in 
the family, while the index of modification undergoes little 
change. 



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No- 567] EFFECT OF DISTRIBUTION ON SPECIATION 151 

This leads ns to a consideration of the factors involved 
in the differentiation of genera as contrasted with the 
differentiation of species. In general it may be said that 
extrinsic modifications, i. e., those which are in some way 
connected with changes in temperature, humidity, char- 
acter of flora, food, and other environmental conditions, 
and which usually affect such characters as color, size, 
length of hair, etc., lead to differentiation of species and 
subspecies primarily. On the other hand, intrinsic modi- 
fications, i. e., those which are related directly or indi- 
rectly to a change in the habits or mode of life of the 
animal or the occupation of a new niche in nature, usually, 
if not always, lead to generic or family differentiation, 
since it is evident that changes fitting an animal to live 
arboreally instead of terrestrially, for instance, are of 
such a nature, that if they are perpetuated and carried to 
perfection, will not stop at specific difference but will 
become of generic importance. 

It might be argued that there are no modifications which 
might not, if carried far enough, ultimately lead to generic 
differentiation. This is possible, but very improbable, 
because the modifications here alluded to as ** extrinsic*^ 
are of such a nature that in the varying climatic condi- 
tions there are likely to be intermediate forms which make 
the division of the more widely separated ones into genera 
impracticable. In the case of our *4ntrinsic*' modifica- 
tions, intermediate forms are not so likely to exist when 
once the incipient changes leading to an altered mode of 
life have reached a fair degree of perfection. 

As a concrete example of what is meant by extrinsic 
and intrinsic modifications, let us take the squirrels of a 
given region, say eastern North America. There are four 
genera to be distinguished, — Sciurius, Tamias, Sciuro- 
pterus and Arctomys. The genus Sciurus contains 
strictly arboreal, mostly nut-eating, omnivorous forms. 
Tamias includes forms which are terrestrial, diurnal, 
dwelling in natural or artificial holes and crevices, and 
with a device for carrying food in their cheeks. Sciuro- 



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162 THE AMERICAN NATURALIST [Vol. XLVHI 

pterus is an arboreal tjrpe which is nocturnal, and has de- 
veloped characters which enable it more easily to travel 
from tree to tree. Arctomys is the most highly modified 
form, and has departed most widely in its habits; it is 
entirely terrestrial, seeks shelter in artificial burrows, 
eats, grass, and hibernates. 

Were we to study the characters separating these gen- 
era, we should find that they are all characters which 
enable the animal best to occupy the ecologic niche it fills. 
If now we select any one of these genera and examine its 
species, we perceive that the differences we find are not 
such as could clearly be related to differences in mode of 
life or habits, but rather such differences as are induced 
by the circumstances mentioned above, such differences 
being size, color, length of feet and tail, texture of fur, 
etc.-i. e., extrinsic variations. 

An interesting example of both extrinsic and intrinsic 
modii&cations in an incipient stage may be foxmd in the 
song-sparrows of western United States. Let us compare 
the form of the humid northwest coast belt, Melospiza 
melodia morphna, with the form of the arid Arizona des- 
erts, M. m. fallaaj. The differences to be observed in color 
and size are very noticeable, and would undoubtedly lead 
to their separation into two distinct species were it not for 
the complete chain of intermediate forms. But even if the 
chain of intermediate forms were not complete, and after 
a period of segregation the numerous intergrading sub- 
species became broken up into a few well-marked species, 
nevertheless, unless a change in mode of life of the bird 
were involved, however far the extremes of color and size 
might tend, they could not be given generic distinction 
because of the intermediate forms, inhabiting semi-arid or 
semi-humid regions, which would be almost certain to 
exist It hapens, however, that Melospiza melodia mor- 
phna, and M. m. fallax, do differ considerably in mode of 
life, the former being a beach comber, the latter a nomad 
of the desert It would be expected, therefore, tiiat if 
these two subspecies were isolated, the modifications re- 



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No. 567] EFFECT OF DISTRIBUTION ON SPECIATION 163 

lated to their difference in mode of life, already shown 
in an incipient manner, woxdd soon lead to their generic 
differentiation. 

It is not argaed that nnder a given set of ecologic con- 
ditions, only one type could be produced, nor that accord- 
ing to the idea of some zoologists, as set forth and refuted 
by Grinnell and Swarth (1913), should individuals of one 
geographic race be transplanted into the region of a dif- 
ferent geographic race, the first race would assume within 
a few generations all the characters of the second race. 
Whether the changes due to the influence of the environ- 
ment be looked upon as the results of natural selection 
and adaptation, or merely as the results of a stimulus to 
the germ plasm, the new type would not necessarily be 
always the same, this, however, depending upon the num- 
ber of potential responses in the type, and, as excellently 
shown by Buthven (1909) in his study of evolution in the 
genus Thamnophis, upon the modifications previously 
undergone by the type we are dealing with. 

It is very evident that there are many variations in 
animals which seem to fall into neither the extrinsic nor 
intrinsic category, but which are neutral and vary inde- 
pendently of climate or habits, and may be inherited phy- 
logenetic tendencies. It is very largely due to these 
neutral variations, frequently to be ascribed to ortho- 
genetic evolution, tending in different directions in dif- 
ferent places, and giv^i an opportunity to diverge by iso- 
lation, that different species may be produced to occupy 
regions of similar climatic and environmental conditions, 
and different genera may be found occup3dng the same 
ecologic niches. 

To choose an example in the same family quoted before, 
we may cite the case of Tamias in eastern North America, 
and Eutamias in western North America. In this case the 
characters separating the genera are not clearly related 
to their mode of life, the chief difference being the loss of 
one small premolar in Tamias, and its retention in Euta- 
mias. The extent of divergence of these neutral varia- 



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154 THE AMERICAN NATURALIST [Vol. XLVIH 

tions depends on the duration of geographic segregation, 
and may therefore be of specific, generic, family, or ordi- 
nal rank. 

To sum up, specific modifications may be of three kinds : 
(1) extrinsic modifications, induced by changes of climate 
and environmental conditions; (2) neutral modifications, 
due to a different trend of evolution in segregated regions ; 
(3) incipient generic modifications. On the other hand, 
generic modification may be either intrinsic modifications, 
concomitant with changes in mode of life or habits of the 
animal, or neutral modifications as above, given generic 
value by a longer i>eriod of segregation. 

Having dwelt for some length on these preliminary con- 
siderations, let us now apply them to the case in hand and 
see how they affect differentiation into species and genera 
through extension of range. 

It is a well-known biological fact that different types of 
a group of animals, at least of higher animals, are found 
associated with different ei^vironments ; nearly related 
species do not, as a rule, live comfortably together in the 
same environment, and nearly related genera do not 
occupy the same ecologic niche in a given zoogeographical 
area. This does not seem to hold true for animals of 
lower organization, as conclusively shown by Kofoid 
(1907). It is common for a group of animals, unless hin- 
dered by an impassable barrier or unfavorable environ- 
mental conditions, not only to continually extend its range 
into new territory, but also to attempt to live in as many 
different niches in nature as possible within a given area. 
Such attempts to invade new ecologic niches are frequently 
concomitant with heritable modifications better fitting 
them to occupy their new situation, though it is difficult to 
say whether these modifications are causes or results of 
the change in mode of life. However this may be looked 
upon, the tendency to occupy new niches in nature is fre- 
quently accompanied by intrinsic modifications, and there- 
fore by generic differentiation. 

From this we may safely assume that in a given area 



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No. 567] EFFECT OF DISTRIBUTION ON SPECIATION 155 

a family of animals, by adaptive evolution, will approach 
a maximum of generic differentiation which can be sup- 
ported in that area. In other words, every suitable eco- 
logic niche which is represented in the region considered 
will be invaded by the family, and even in a small area 
there is likely to be a considerable generic differentiation, 
especially if isolation has had any opportunity to operate 
within the area, in breaking up the genera and species. 

Let us assume that in one unit of area a certain family, 
Sciuridae for example, was represented by three genera, 
each with three species. Second, let us assume that this 
family kept spreading into additional units of area. With 
each new unit, the chance of new suitable ecologic niches 
being represented would decrease, and therefore the 
chance of new genera being represented would decrease, 
since if a genus were fitted for its niche in nature imder 
certain conditions of climate and environment, it would 
in the majority of cases not be likely to undergo any 
radical changes in the occupation of the same niche 
under somewhat altered conditions of climate and environ- 
ment; i. e., the stimulus for intrinsic modification would 
be lacking. 

On the other hand, with each additional unit of area, the 
chances of the combined conditions of temperature, hu- 
midity, and environment being different, would remain the 
same. In other words, the chances of the three dimen- 
sions influencing the life of a region, i. e., **life zone** 
(controlled by temperature), ** fauna'* (controlled by hu- 
midity), and ** association" (controlled by the effect of 
the other two plus a number of other environmental con- 
ditions), intersecting at the same point would be almost 
equally improbable with each succeeding unit of area. 
Since it is changes in *'life zone,*' ** fauna,** or ** associa- 
tion** which produce extrinsic changes, and therefore lead 
to differentiation of species and subspecies primarily, the 
increment of species would average nearly the same for 
each succeeding unit of area, other factors remaining 
equal. It should also be taken into consideration that 



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166 THE AMERICAN NATURALIST [Vol. XL VIII 

with the invasion of new zoogeographic areas, contact 
with allied forms is frequently experienced, and oppor- 
tunity is thus afforded for cross breeding and hybridiza- 
tion, the result of which upon the germ plasm appears to 
be as influential in the production of new forms as is the 
shock of new environmental conditions. The constant 
increase in species and subspecies accompanying invasion 
of new territory, going hand in hand with a diminishing 
increase in genera, results in the constantly larger index 
of modification as the area inhabited by a group is 
extended. 

SUMMABY 

1. Extent of distribution has a direct influence on the 
speciation of the group concerned in this way, that as the 
range of a group of animals is extended, the species in- 
crease out of proportion to the genera, the genera out of 
proportion to the families, and the families out of pro- 
portion to the orders. 

2. Comparisohof different families having unequal geo- 
graphic ranges is usually inaccurate due to the great dif- 
ferences in the other factors controlling their speciation. 
Those families which do lend themselves to such a com- 
parison show decidedly the effect of extent of distribu- 
tion, e. g., the bats and some of the insectivores, the fami- 
lies of widest distribution having the largest indices of 
modification. A number of exceptions exist in the form of 
certain wide ranging genera which have a paucity of 
species. We have no adequate explanation for this 
phenomenon. 

3. Comparison of the faunas of areas of different size 
gives very accurate results. A number of tabulations show 
as a whole an invariable increase in the index of modifica- 
tion as the distributional area is extended by the addition 
of either life zones, faunas, or associations. Such tabu- 
lar comparisons were made for all the classes of ter- 
restrial vertebrates, for several families of insects, and 
for the marine Amphipoda of the suborder Gammaridea. 
Allowing for explicable exceptions, the increase in number 



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No. 567] EFFECT OF DISTRIBUTION ON SPECIATION 167 

of lower systematic groups out of proportion to the in- 
crease of higher systematic groups as the area considered 
is enlarged is a remarkably constant and wide-spread 
phenomenon. 

4. The theoretical explanation here proposed for this 
phenomenon involves a number of complex problems 
relating to evolution and speciation, including isolation^ 
the time element, and causes of specific and generic 
modification. 

5. Isolation is an important factor in speciation, since 
the separation of species into two or more parts allows 
the parts to become different The degree of divergence 
of the s^regated parts is largely dependent upon the 
duration of segregation. 

6. Time, in conjunction with isolation and evolution, 
tends to increase the number of genera and species in a 
family, but the index of modification, t. e., the average 
number of species per genus, remains approximately the 
same in a given area. 

7. Three types of modifications in animals may be 
named:— first, ** extrinsic'* modifications, which are in- 
duced by climate and other environmental conditions, and 
which lead to differentiation of species and subspecies 
primarily; second, ** intrinsic'' modifications, which are 
concomitant with a change in habits or mode of life of the 
animal, due to the occupation of a new ecologic niche, and 
which usually lead to generic or family differentiation; 
and third, neutral. modifications, which are merely the 
result of the natural tendency of all animals to vary and 
to be subject to more or less orthogenetic evolution,— 
modifications which can not be correlated with environ- 
mental conditions, nor with a change in mode of life of 
the animal, but which may be influenced largely by in- 
herited tendencies. Such modifications are responsible for 
the production, through isolation, of different species to 
live under the same climatic and environmental conditions, 
and of different genera to occupy the same ecologic niche. 

8. Specific modifications may be of three kinds: (1) ex- 



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168 THE AMERICAN NATURALIST [V0L.XLVIII 

trinsic modifications, (2) neutral variations in segregated 
regions, ( 3 ) incipient generic modifications. Generic modi- 
fications may be (1) intrinsic modifications, or (2) neutral 
varations, given generic value by a longer i)eriod of 
segregation. 

9. Since different types of a group of animals are 
usually found associated with different environmental con- 
ditions or different ecologic niches, and since it is common 
for animals, if unhindered, not only to extend their range 
continually into new territory, but also to occupy new 
ecologic niches, and since these tendencies lead to specific 
and generic differentiations, respectively, any given area 
will have a differentiation of species proportionate to its 
variety of environmental conditions, and of genera pro- 
portionate to its variety of suitable ecologic niches. 

10. Since, as the area of distribution is extended, the 
chance of new conditions of climate and environment being 
represented remains approximately the same, the increase 
in number of species is nearly proportional to the increase 
in the area of distribution, but since the chance of new 
ecologic niches being represented in most cases constantly 
decreases, the increase in genera proceeds at an ever- 
diminishing rate. This, going hand in hand with the 
nearly constant increase in species or subspecies, results 
in a constantly increasing index of modification. 



LITERATURE CITED 
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Darwin, Ch. 

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xi, 440, 1 pi. 
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Dreflser^ H. E. 

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1908. The Biota of the San Bernardino Mountains. Uniy. Calif. PabL 

Zool., 5, 1-170, pis. 1-24. 
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Acad, Set,, 4tli series, S, 265-390, pis. 15-16. 
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Grinnell, J.^ and Swarth, H. S. 

1913. An Aeconni of the Birds and Mammals of the San Jacinto Area 
of Southern California, with Bemarks upon the Behavior of 
Geographic Baces on the Margins of their Habitats. Vjoy, 
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1912. A Handlist of British Birds. London, Witherby & Co., XII, 237. 
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1912. A List of the Mammals of the Philippine Islands, EzclusiTe of the 
Cetacea. Phihpp. J. Set., D, 7, 1-64. 
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1901. The Limitations of Isolation in the Origin of Species. Science, 
N. S., es, 500-606. 
North, A, J. 

1901-1909. Nests and Eggs of Birds Found Breeding in Australia and 
Tasmania. Austr. Musi, Sydney, Sp. Catalogue I, Vol. 1, vii, 
366, pis. A 1-8, B 1-7, text figs.; Vol. 2, vii, 380, pis. A 9-13, 
B 8-13. 
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1908. A Handlist of the Birds of Japan. Annot. Zool. Jap., Tokyo, (>, 

337-420. 
de Bothschild, W., and Jordan, K. 
1907, Lepidoptera, F^m. Sphingids. Genera Ineectorum (ed. by Wyts- 

man. P.), 57, 157, 8 col. pis. 
Buthven, A. G. 

1909. A Contribution to the Theory of Orthogenesis. Aic. Nat., 43, 

401-409. 
Bchwarz, O. 

1906. Coleoptera, Fam. Elateridee. Genera Insectorum (ed. by Wytsman, 
P.), 46, 370, 6 col. pis. 
Sclater, W. L., and Sclater, P. L. 
1899. The Geography of Mammals. London, Eegan Paul, Trench, 
Trubner & Co., xviii, 335, 8 maps, 51 figs, in text. 
Stebbing, T. B. B. 
1906. Amphipoda. I. Gammaridea. Das Tierreich (ed. by F. E. 
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Stpjneger, L. 
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and in Kamtschatka. Smithsonian Inst. Nation. Mus. Bull., t9, 

382, 8 pis. 
Tower, W. L. 

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Leptinotarsa, Washington, Cam. Inst. Publ., 4^, x, 321, 30 pis., 
31 figs, in text. 
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13 col. pis., 28 black pis. 
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BIOLOGY OF THE THYSANOPTEBA^ ^ 
DR. A. FRANKLIN SHULL 

XJNIVEBSITr OF MlOHIOAN 

I. FACTORS GOVERNING LOCAL DISTRIBUTION 

Intboduction 

The Thysanoptera, commonly called thrips, are only 
beginning to be known, in this conntry, by systematic 
entomologists. The systematic knowledge is mostly con- 
tained in the monograph of Hinds (1902), a more recent 
synopsis by Monlton (1911), and a few other papers deal- 
ing with new species and with relationships, prominent 
among which is the work of Jones (1912). Biologically 
the group is still less known. A considerable number of 
papers have been issued from experiment stations, de- 
scribing the life history {egg^ larval, pupal and adult 
stages) and habits of thrips of economic importance. Be- 
sides these the principal recent work of a biological 
nature is a paper of my own (Shull, 1911), on the ecology, 
method of locomotion, mode of reproduction, and dissemi- 
nation. The life cycle of most species is still largely un- 
known« 

The first section of this paper is an attempt to carry 
into further detail the study of the ecology of the Thy- 
sanoptera. The first ecological scheme, so far as I am 
aware, worked out for the Thysanoptera was that of Jor- 
dan (1888), who divided thrips into three classes: first, 
the flower-dwellers ; second, the leaf -dwellers ; and third, 
all other thrips (for example, those living on fungi, under 
wet leaves, under bark of trees, on roots, on lichens, etc.). 
The inadequacy of this classification, and the difficulty of 
applying schemes of ecology adapted to other groups of 
insects, was pointed out in my earlier paper, where I pro- 

1 GontributionB from the Zoological Laboratory ot the Uniyersity of 
Miehigaiiy No. 142 (Biological Station Series, Zoological Publication, 
No. 10). 

161 



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162 THE AMERICAN NATURALIST [VouXLVHl 

posed a new scheme, based on my observations in the 
field. In this scheme, Thysanoptera were divided into 
two groups : (1) interstitial species, those living in closely 
concealed situations, as among the florets of composite 
flowers, or in clusters of young leaves; and (2) super- 
ficial species, those living on exposed surfaces, for ex- 
ample, the surface of leaves. The interstitial species 
were further divided into an anthophilous division 
(flower-dwellers) and a phlceophilous division (those 
living under bark scales on trees). The superficial spe- 
cies were either poephilous (on grass) or phyllophilous 
(on leaves of plants other than grasses). The distinction 
between poephilous and phyllophilous seemed warranted, 
since grass-dwellers were found on many different 
grasses, but rarely on other kinds of leaves. 

Such a classification undoubtedly describes the facts, 
but does not explain why the habitats named are the ones 
chosen(f). The factors determining habitat were be- 
lieved by me at that time to be character of food, and pro- 
tection afforded. In some species one of these factors 
predominated, in other species the other factor, while 
others may have been influenced largely by both. In the 
light of recent ecological studies, however, the explana- 
tion of local distribution in terms of such general environ- 
mental factors seems inadequate. Largely owing to the 
work of Shelf ord (1911) upon the tiger-beetles, much 
emphasis is now being placed upon the ecological impor- 
tance of physiological factors. With a view to relating the 
distribution of Thysanoptera to the physiology (more 
specificially, behavior) of the various species, and thus 
explaining that distribution in more definite terms, the 
experiments and observations recorded in this paper 
were made. 

This work was done largely at the University of Michi- 
gan Biological Station, at Douglas Lake, Michigan, sup- 
plemented by observations at Ann Arbor, Michigan, in 
Ohio and elsewhere. 



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No. 567] BIOLOGY OF THE THTSANOPTEBA 163 

Facts to be Explained 

The following are some of the facts of habits and dis- 
tribntion of the more abnndant species for which physio- 
logical explanations were sought. Some of these facts 
are stated in my former paper, some of them doubtless 
the common property of all thysanopterists ; others, so 
far as I know, have never been recorded. 

Euthrips tritici is found almost exclusively in situa- 
tions where it is concealed, as among the florets of com- 
posite flowers, in clusters of young leaves, or in almost 
any close crevice where the tissues are not too hard or 
tough to be pierced. It appears to make little difference 
what species of plant is inhabited, provided a concealed 
situation is available. In the paper cited above (Shall, 
1911) I gave a list of seventy species of plant on which 
Euthrips tritici was taken, and I have since collected it on 
a number of plants not included in that list. But with 
rare exceptions, it has been found in crevices where it was 
not readily visible. In related plants, it is always more 
abundant in those affording concealed situations. Thus, 
in white clover {Tri folium repens) and in red clover 
(jT. pratense)y this thrips is usually abundant; while on 
the related yellow, and white, sweet clovers (Melilotus 
officinalis and M. alba, respectively), growing along with 
the red and white clovers, Euthrips tritici is usually rare 
or wanting. The flowers of Melilotus are widely sepa- 
rated from one another on the stem, and do not afford 
concealment (ShuU, 1911). 

If, while Euthrips is in one of these crevices, it is dis- 
turbed, as by gently rubbing or pressing the flower, it 
quickly comes out of its retreat and crawls rapidly away, 
or takes to flight. The larvae show the same behavior as 
the adults in this regard, except, of course, that they do 
not fly. 

Anaphothrips striatus is found usually on grasses of 
various kinds, rarely on leaves of other plants. The spe- 
cies of grass seems to make little difference. Some indi- 
viduals are found in perfectly exposed situations, as on 



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164 THE AMEBIC AN NATURALIST [VoL.XLVin 

the upper side of grass blades, others more or less con- 
cealed in the rolled up young leaves (Shnll, 1911). I have 
found, however, that among the adults, those in exposed 
situations are almost exclusively females, while those in 
the rolled young leaves are either males or females. (For 
the first time on record, the males of this species, as will 
be shown in the second part of this paper, have been found 
in considerable numbers.) The larvsB, according to my 
observations, may be either exposed or concealed; the ex- 
posed ones are predominantly the older larvae. 

In one of the grasses {Spartina michauxiana) on which 
Anaphothrips was found in abundance at Douglas Lake, 
Michigan, the leaves bear on the upper surface a set of 
fine, but prominent, ridges running parallel to the axis of 
the leaf. Adult females and larvae of Anaphothrips on 
the exposed parts of these leaves were always lodged be- 
tween the tops of these ridges, and almost invariably 
unth their heads toward the base of the leaf. If disturbed, 
they began to crawl along the crest of one of these ridges 
toward the base of the leaf. It was possible to force them 
to turn in the opposite direction, but if allowed to do so 
they soon turned again toward the base of the leaf, often 
continuing until they were among the rolled young leaves 
in the center of the top of the plant. 

Anthothrips verbasci is found exclusively on one spe- 
cies of plant, the common mullein {Verbascum thapsus). 
Furthermore, it is rare that a specimen of mullein, of con- 
siderable size, is found free from the mullein thrips. Most 
of the thrips are found among the florets or seed pods of 
the spike. Less commonly they are to be seen on exposed 
surfaces, as on the leaves or stem lower on the plant; but 
these exposed individiials are mostly adults. The larvse 
are usually hidden on the flower sp^e unless that situa- 
tion is crowded by a large number of larvae ; and the larva 
that are occasionally found exposed are mostly nearly 
fully grown. 

Anthothrips niger was not abundant enough during my 
stay at Douglas Lake that many observations of its 



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No. 567] BIOLOGY OF THE THTSANOPTEBA 165 

habitat and behavior could be made. One f act, howeyer, 
is of interest in connection with an experiment to be de- 
scribed. While the adults live mostly on flowers, some- 
times concealed, sometimes more or less exposed, the 
larv» were always found concealed; moreover, it was 
ivith difficulty that the larva could be driven from their 
retreat by pressing the flowers. Frequently such vigor- 
ous squeezing was necessary to dislodge them that the 
larv® emerging were injured ; and a flower so treated was 
often found later to contain numerous dead larvsB. In 
this respect, the behavior of this species is in considerable 
contrast to that, for example, of Euthrips tritici. 

The habitats and behavior described above can be ^^ex- 
plained'' in large measure if we say, as I at first proposed 
(1911), that certain species seek protection, or that cer- 
tain other species have specific food requirements. Thus, 
it might be said that Euthrips tritici seeks safety in 
crevices, and flees danger when disturbed ; that Anapho- 
thrips striatus ** prefers'' grass for food, that it requires 
as much protection as its commissarial activities permit, 
and that its habitat and behavior are such as best fulfill 
these requirements. Anthothrips verbasci might be said 
to be limited to one article of diet, while protection is a 
minor matter. 

This explanation might be acceptable as far as it goes, 
were it not that no species is immune to attack. I have 
seen larvae of Anthothrips verbasci frequently captured 
by various bugs. Heads of mullein where thrips are 
found nearly always bear bugs of the family Capsidae, 
and observations convince me that they prey almost 
wholly on the larvae of the mullein thrips. The degree to 
which they check the thrips was tested experimentally as 
follows : Two mullein spikes of approximately equal size 
and equally infected with thrips were selected. The 
predatory bugs were removed from one of them, after 
which the spike was enclosed in a thin muslin bag. Two 
weeks later the bag was removed. The enclosed spike 
bore a large number of full-grown larvae, a few had 



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186 THE AMERICAN NATURALIST [Vol. XLVni 

pupated, and many were crawling on the inside of the 
bag. The spike that was exposed, on the other hand, bore 
but little over half the number of larvae that were on the 
protected one, none were quite full grown, and none had 
pupated. Since nothing in the climatic conditions (heavy 
rains, for example) could have caused this difference, 
it is to be inferred that predatory bugs had devoured the 
larger larvae in considerable numbers. 

Yet Anthothrips verbasci, according to my earlier ex- 
planation, ** chooses'' its habitat almost exclusively in re- 
lation to food, protection being a minor consideration. 

Can we not explain habitat and behavior in these in- 
sects in some way not implying choice, especially choice 
between conflicting preferences ? May we not assume that 
certain elements of behavior are what they are without 
reference to their usefulness? If we grant the possibility 
of an aflSrmative answer to these questions, the experi- 
ments about to be described will have significance. 

Experiments on Behavioe 
The following experiments were designed to show the 
reaction of the commoner species of Thysanoptera to 
what seemed to me the most probable external agents 
affecting their distribution and behavior, namely, light, 
contact and gravity. Inasmuch as I was not primarily 
interested in how a given reaction was brought about, but 
only in its end result, the experiments were rather crude. 
Eefinements were unnecessary, and their omission en- 
abled me to use much greater numbers of individuals than 
would otherwise have been possible. From ten to forty 
repetitions of each test were usually made. The experi- 
ments are described by species, only representative ex- 
periments being given. 

Euthrips tritici 
Light. Exp. 1. — ^Adults of this species were placed in 
a glass tube about three feet long and one inch in diam- 
eter, closed at the ends with corks. One end of the tube 



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No. 567] BIOLOGY OF THE THTSANOPTERA 167 

was turned toward a small window, while the room was 
rather dimly lighted. All the thrips crawled rapidly 
toward the window. When the position of the tube was 
reversed, the thrips reversed their crawling, again going 
toward the iraidow. The reaction was definite and in- 
variable. 

Exp. 3. — ^A close-fitting sleeve of black building paper 
was slipped over one half of the glass tube used in experi- 
ment 1. The thrips were collected at the exposed end by 
turning that end for a few minutes toward the window. 
The covered end of the tube was then turned toward the 
window. The thrips crawled rapidly toward the light, 
until they reached the shadow of the sleeve. Here they 
crawled about, apparently aimlessly, for half an hour an 
inch or two within the sleeve or just outside it. 

Contact. Exp. 1. — ^When, in the light experiments, the 
tube was reversed in position as soon as the thrips 
reached one end, the insects immediately turned toward 
the opposite end. But if the tube was allowed to rest for 
some time, the thrips became settled quietly between the 
glass and the sloping surface of the cork. The tube could 
then be carefully reversed, and most of the thrips re- 
mained lodged between cork and glass for many minutes, 
some of them for hours. The positive reaction to contact 
counteracted the positive reaction to light. 

Exp. 25. — ^A larva of this species was placed on a glass 
plate, upon which rested a microscope slide. When the 
larva in its crawling reached the slide, it came to rest in 
the angle formed by the glass plate and the edge of the 
slide. It remained there many minutes until disturbed. 

Gravity. Exp. 17. — ^An adult female was placed in a 
glass tube which was enclosed in a black sleeve to exclude 
Ught, and the tube placed in a vertical position. The posi- 
tion of the thrips was marked with a wax pencil before 
putting on the sleeve. The sleeve was then removed mo- 
mentarily at frequent intervals, and the position and 
direction of crawling of the insect noted. Most fre- 
quently it was found lower than the previous position. 



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168 TRE AMEBIC AN NATURALIST [Vol. XLVHI 

and crawling downward. This was not always the case, 
however. 

Of other specimens tried, some showed positive geo- 
tropism more definitely, some less definitely than the one 
described. None showed a negative reaction in the ma- 
jority of cases. 

Anaphothrips striatus 

Light. Exps. 5 and 7. — ^Adnlts of this species were 
shaken ont on a sheet of white paper near a window, and 
the course of their crawling was plotted as accurately as 
possible in my notes. Some individuals were decidedly 
negative to light, crawling directty away from the window 
every time they were tried, regardless of the direction in 
which they happened to be headed when they touched the 
paper. Others were indifferent to light, crawling in vari- 
ous directions. Most of the males used were decidedly 
negative to light, females usually indifferent. 

Exp. 10. — ^Females taken from the exposed portions of 
leaves of Spartina michauxiana, and tested as above, 
were found in nearly every case to be indifferent to light. 
Females from the curled young leaves of the same plants 
were as a rule negative to light. 

Exp. 6. — ^Larvae were usually found indifferent to light, 
regardless of whether they came from exposed or con- 
cealed situations. 

Exp. 15. — ^A single larva taken from the exposed part 
of a leaf, when placed in a glass tube one end of which 
was directed toward the window, crawled steadily toward 
the window. When the position of the tube was reversed, 
the larva at once reversed its direction. The tube was 
then placed in a black sleeve to exclude the light, and kept 
there for an hour. When it was removed, the larva 
showed for some minutes a decidedly negative reaction to 
light. Later, however, its behavior became indefinite, 
and soon became markedly positive. Darkness had ap- 
parently temporarily reversed its reaction. 

Contact. Exp. 22. — ^A female of this species which was 



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No. 567] BIOLOGY OF THE THJSANOPTEBA 169 

negative to light was placed on a sheet of blotting paper. 
A small square of glass was placed over her, and sup- 
ported at one edge, so that in crawling away from the 
window the thrips approached the edge of the glass which 
was in contact with the paper. She soon became lightly 
wedged between the glass and the blotter, and came to 
rest. Blotter, thrips and glass were tiien carefully 
turned through 180 degrees so that the negative reaction 
to light would have led the thrips out of its crevice; but 
she remained there for a long time. Positive reaction to 
contact overcame the negative reaction to Ught. 

Another female, indifferent to light, was placed under 
a sinoilar glass. In her random crawling she became 
wedged between the blotter and glass, and, notwithstand- 
ing that the blotter was occasionally turned in the mean- 
time, remained there several hours, until I lifted the glass. 

Another female, not negative to light, was placed under 
a similar glass square. She crawled from under it, but 
happened to crawl against the edge of the microscope 
slide that supported the glass cover. She settled quickly 
into the right angle formed by the slide and the blotter, 
and remained there a long time. 

Gravity. Exp. 21. — ^A female which was indifferent to 
light was placed in a glass tube, and the tube set in a 
vertical position. The thrips immediately began to crawl 
downward. The tube was reversed, and the thrips im- 
mediately reversed its direction. A sleeve was placed 
over the tube to exclude the light, and frequently removed 
temporarily to observe the position of the thrips. In 
every case she was found crawling downward. 

"Wlien the tube was held in an oblique position, the re- 
sult was the same ; the thrips crawled down the slope. If 
she was already crawling down, a slope of 5 to 10 degrees 
was found to be sufficient to keep her going in the same 
direction. But to reverse the direction of crawling, it 
was necessary to create a slope of about 45 degrees in the 
opposite direction. The same positive geotropism was 
shown when the thrips was placed on an inclined sheet of 



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1 70 THE AMERICAN NATURALIST [Vol. XLVUI 

paper; but being here at liberty to fly, she soon inter- 
rupted the experiment. 

Numerous other females were tried, and all showed 
positive geotropism, some more promptly than others, 
but all perfectly definitely. A single male tested showed 
no definite reaction to gravity. A larva, nearly full 
grown, subjected to the same tests, showed as definite a 
positive reaction to gravity as did any of the females. 

With the possible exception of the males, therefore, 
Anaphothrips striatus is decidedly positive to gravity. 

Anthothrips verbasci 

Light. Exp. 4. — ^Adults of this species, shaken out on 
a paper near a window, crawled in various directions. 
None of them showed any definite reaction to light. 

Numerous larvae, none of them over three fourths 
grown, crawled directly away from the window in every 
instance. 

Exp. 12. — ^In this experiment adults from concealed 
places in mullein spikes were compared with those from 
exposed situations. They were shaken out on a sheet of 
paper near a window, and the direction of crawling noted. 
In every case, those from concealed situations showed a 
fairly definite negative reaction to light. Of those from 
exposed situations, two were plainly negative, the re- 
maining ten indifferent to light. 

Exp. 11. — ^Larvae taken from concealment in a mullein 
spike were tested, on a sheet of paper, for their reaction 
to light. Those of the smaller sizes crawled directly away 
from the windoiv. Those nearly full grown, while on the 
whole negative, crawled in a more or less devious path 
away from the window;. One reddish larva, which from 
its color and size must have been nearly ready to pupate, 
was especially indefinite in its reaction to light. 

Contact. Exp. 18. — ^Larvae of various sizes, which were 
found to be negative to light, were placed on a blotter 
under a square of glass supported at one edge, as de- 
scribed for Anaphothrips striatus. When, in crawling 



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No. 567] BIOLOGY OF THE THTSANOFTERA 171 

away from the window, they became wedged lightly be- 
tween glass and blotter, and came to rest, the blotter with 
all on it was turned through 180 degrees. The larvae 
turned their bodies so that their heads were directed away 
from the window, but did not crawl away. The positive 
reaction to contact overcame the negative response to 
light. 

An adult tested in the same manner as the larvae above 
described did not come to rest under the glass square. 
But happening to crawl against the microscope slide 
which supported the glass, the thrips came to rest in the 
right angle formed by the blotter and the edge of the 
slide, and remained there a long time. 

Gravity. Exps. 13 and 20. — ^Adults and larvae were 
put, one at a time, into a glass tube, which was set in a 
vertical position, and covered with a black sleeve to ex- 
clude light. Some were examined at frequent intervals, 
others were left half an hour without examination. In 
every case the thrips were found almost precisely where 
they were put at the beginning of the experiment. This 
species is therefore indifferent to gravity. 

Anthothrips niger 
Light. Exp. 2. — The red larvae of this species were 
shaken out on a paper near a window, as described in 
other experiments. In every case the larva crawled away 
from the window for a few seconds at firsts then slowly 
turned toward the window, and continued indefinitely 
toward the light. Once while the larva was crawling 
toward the light, I tapped the paper vigorously with a 
pencil, so that the thrips was lifted slightly from the 
paper and let drop; it immediately reversed its direction, 
crawling from the window, but in a few seconds turned 
again toward the light. The paper was jarred frequently, 
but always with the same result. To show whether the 
jarring made the response to light negative, or merely 
reversed whatever the larva was doing at the instant, the 
tapping was repeated at intervals of one or two seconds. 



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172 THE AMERICAN NATURALIST [VoL.XLVni 

At the first tap, the larva, which had been crawling 
toward the window, immediately tnmed away from the 
light. Before it resumed its positive response to the light, 
the paper was tapped again ; the negative response con- 
tinued. In this way the larva conld be kept crawling away 
from the light indefinitely. Disturbance makes the reac- 
tion of the larva to light temporarily negative; otherwise 
it is positive. 

Summary op Expbeimbnts 

Euthrips tritici, when disturbed, is positively photo- 
tropic in both larval and adult stages. It is positively 
stereotropic, and the stereotropism is stronger than pho- 
totropism, at least under certain circumstances. Some 
individuals appear to be on the whole positively geo- 
tropic ; others are indiflPerent. 

Anaphothrips striatus. — ^Adult males are usually nega- 
tively phototropic. Females taken from exposed situa- 
tions are usually indifferent to light, those from concealed 
situations usually negative. The larvae are usually in- 
different to light, regardless of the kind of place from 
which they are taken ; a single larva that was positive was 
made negative by keeping it in the dark. Adults are posi- 
tively stereotropic. The females and larvae are positively 
geotropic. 

Anthothrips verbasci. — ^Adults taken from concealed 
situations are usually negatively phototropic, those from 
exposed places tend to be indifferent to light. The larvae 
are all negatively phototropic, except the full-grown ones, 
which may be indifferent. The larvae are plainly posi- 
tively stereotropic, the adults less plainly so, or not at all. 
Neither adult nor larva responds to gravity. 

Inteepbetation op the Experiments in thbib Bblation 
TO Distribution and Behavioe op Thrips in Nature 
With the evidence from these experiments before us, 
may we not interpret the observed distribution and be- 
havior of the Thysanoptera in nature somewhat as fol- 
lows ? Instead of explaining the fact that Euthrips tritici 



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No. 667] BIOLOGY OF THE THTSANOPTEBA 173 

always lives in concealed situations as due to a demand 
for protection, we may assume that it is due to the strong 
positive stereotropism of this species — aided in some 
cases by positive geotropism, where the flower inhabited 
is upright, but notwithstanding positive geotropism 
where the flower is inverted. The rapid escape by crawl- 
ing or flight when disturbed is not due to the fact that 
this is the best way of avoiding danger, but to the posi- 
tive reaction to light. Other species avoid danger by 
going deeper into crevices, because they are negatively 
res]>onsive to light. 

Anaphothrips striatus lives on grasses doubtless be- 
cause it can not live on any other food, or because the 
reproductive processes are not stimulated by any other 
host plant. But their distribution and behavior on the 
grasses may be explained largely in terms of their reac- 
tions to the three agents tested in the experiments. The 
males usually live in concealed situations on the plants 
(curled-up leaves) because they are mostly negatively 
phototropic, and crawl down the leaves until they reach 
these concealed situations. Females may live either in 
exposed or in concealed places, for some of them are 
negative to light, others indifferent. The larvae are either 
exposed or concealed, because they are indifferent to 
light. The eggs from which they hatch are probably laid 
by negatively phototropic females in the young curled 
leaves, and tiie leaves unfold as the larvsB develop; this 
explains why the exposed larvsB are much larger, on the 
average, than are those concealed in the young leaves. 
Perhaps the relation of cause and effect as here stated is 
reversed, at least for some cases. Concealment — caused 
in one way or another — ^may lead to negative phototro- 
pism, as in the larva which was made temporarily nega- 
tively phototropic by being kept in the dark. 

The adults are lodged between the ridges on the upper 
side of the leaves of the grass Spartina, not for the sake 
of protection, it seems to me, but because they are posi- 
tively stereotropic. Doubtless between the ridges is the 



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174 THE AMEBIC AN NATURALIST [Vol. XLVni 

place where they can best suck the juices of the plant, but 
there is no need to assume that they deliberately choose 
this location in order to get their food most easily. Both 
adults and larvae rest on these leaves with their heads 
directed toward the base of the leaf, and crawl toward 
the base of the leaf if disturbed, not because protection is 
most quickly to be found among the curled leaves at the 
center of the plant, but because the thrips are positively 
geotropic. 

Anthothrips verbasci. — The larvae of this species live 
hidden among the flowers of the mullein spike, not be- 
cause they must get their food there, for they can get it 
from any part of the plant; nor do they hide there, it 
seems to me, to secure protection. They remain in these 
crevices because, excepting the largest larvae, they are 
positively stereotropic and negatively phototropic. The 
adults are sometimes exposed, sometimes concealed, prob- 
ably because in the former case they are usually indiffer- 
ent to light, in the latter case negatively phototropic. (Or 
may they be made negative or indifferent according as 
they live — ^f or one reason or another — concealed or ex* 
posed?) 

Thus, while Anthothrips verbasci is limited to one food 
plant, and the food requirements are therefore probably 
exceedingly important, yet the distribution and behavior 
of the insects on this plant may be explained without ap- 
pealing to anything like ** choice*' in other matters. 

Regarding Anthothrips niger, I wish to call attention 
to but one fact. The difficulty with which the larvae are 
driven forth from a flower in which they live appears to 
be due, not to a persistent attempt at concealment, but to 
the fact that on being disturbed they are temporarily 
negatively phototropic; if the disturbance is continued, 
the negative response continues. 

The only argument which, it appears to me, could be 
advanced in favor of assuming that the Thysanoptera 
choose their locations, instead of adopting simple re- 
sponse to external stimuli as the correct explanation of 



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No. 567] BIOLOGY OF THE THTSANOPTEBA 176 

distribution, is the possibility that they have learned that 
certain modes of behavior are best suited (for example) 
to continued safety. 

The reply to such an argument is first, that most of my 
studies on behavior have been made in an unsettled re- 
gion, where the enemies of thrips incident to civilization 
are practically wanting, and where even the natural 
enemies are not abundant. It could hardly be assumed 
that every individual would learn to avoid its enemies in 
the course of its short lifetime, yet certain species seem 
to be invariable in their response to certain agents. 
Furthermore, many of the larvae tested in the experi- 
ments could have been but a few days old. It is incred- 
ible that their reactions should have been, as in fact they 
were, as definite and invariable as those of older larvae, 
if these responses were dependent on experience. 

It seems to me, therefore, that the only satisfactory ex- 
planation of outdoor behavior and distribution of the 
Thysanoptera lies in the assumption that they are in 
large measure the result of responses to simple stimuli, 
and do not imply any degree of choice. 

Obigin and Adaptivenbss op Besponses to External 

Stimuli 

The origin of such responses in Thysanoptera as have 
been described above is not, I believe, discoverable. Pur- 
poseful they most probably are not, as I have shown, if 
by purpose we mean conscious direction of actions to 
some end. But adaptive they no doubt are in many cases. 
Perhaps they are all adaptive, but I confess that my 
powers of analysis are not keen enough to prove such a 
view correct. That Euthrips tritici is positively photo- 
tropic when disturbed is no doubt the cause of frequent 
escapes from danger. One may even believe the negative 
phototropism of larvae of Anthothrips verbasci to be 
adaptive, because they are much more sluggish than is 
Euthrips tritici, and could not escape quickly even if they 
should emerge into the light. They are probably safest. 



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176 THE AMERICAN NATURALIST [VoL.XLVm 

theref ore, if , when disturbed, they retire into still deeper 
crevices. But I am nnable to discover the adaptiveness 
of the response of the larvsB of Anthothrips niger to light 
— at first negative, on being distorbed, bnt soon becoming 
positive. Nor can I understand why the males of Ana- 
phothrips striatus are more definitely negative to light 
than are the females or larvsB. These reactions seem to 
me to be useless. 

We need not demand that all of these responses be 
adaptive, any more than that they be purposeful. Re- 
sponses have arisen, no one knows how. They have been 
preserved, and we can but speculate as to the method of 
their preservation. Natural selection may be respon- 
sible for the preservation of the useful, and it may have 
eliminated res]>onses that were harmful. But other re- 
sponses of no value whatever, but likewise harmless, may 
have been allowed to persist, without help or hindrance 
from selection. 

(To he continued.) 



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SHORTER ARTICLES AND CORRESPONDENCE 

THE ENDEMIC MAMMALS OF THE BRITISH ISLANDS 

When, in 1891, I was collecting information to be used by 
Dr. A. E. Wallace in preparing the second edition of his ''Island 
Life," I found much skepticism among naturalists concerning 
the alleged endemic or precinctive elements of the British fauna. 
Dr. Wallace was able to give lists of supposed precinctive species 
and varieties belonging to several groups, but for the mammals 
he was obliged to state, "it is the opinion of the best authorities 
that we possess neither a distinct species nor distinguishable 
variety." We little imagined that about twenty years later the 
British Museum would issue a work describing ten species and 
twenty subspecies of mammals peculiar to the British Islands; 
twenty-one of these being actually undescribed at the time I 
made my enquiries, and the rest then reposing quietly in the 
synonymy. Still less did we imagine that such a revision, when 
made, would be the work of an American, coming over from the 
United States National Museum to show Europeans the neglected 
wonders of their own fauna ! The Catalogue of the Mammals of 
Western Europe, by Mr. G. S. Miller, published last year by the 
British Museum, is certainly one of the most remarkable zoolog- 
ical works ever produced, and is well worthy of the attention of 
all naturalists, whether specially interested in the Mammalia 
or not. While so many students of genetics are giving us the 
results of their experiments in breeding mammals, it is worth 
while to turn also to the results of nature's long-time breeding 
exx>eriments, so clearly set forth by Mr. Miller in the volume cited. 
What, after all, is the connection between the phenomena seen by 
the breeder and the facts of mammalian evolution t Do species 
and subspecies differ by "units,'' and do the variations observed 
in captivity correspond in any way to the recorded specific and 
snbspecific differences T 

A complete analysis of Mr. Miller ^s volume can not be made at 
the present time, but I have extracted the list, given below, of 
the forms supposed to be confined to the British Islands, giving 
their distribution and principal distinctive characters. I have 
added to Mr. Miller's list three quite recently described animals. 
On examining the list, it appears that a few of the species must 
belong to the older fauna of the country, not wholly exterminated 
by the glacial ice and periods of partial submergence. Such are 

177 



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178 THE AMERICAN NATURALIST [VouXLVm 

Mustela hibemica of Ireland and Microtus orcadensis of the 
Orkney Islands. It is at least suggestive, in this connection, that 
so many of the Scottish islands yield animals differing from 
those of the mainland. In the majority of cases, however, the 
peculiar British mammals are closely related to those of the con- 
tinent, and might well be of very recent origin. There is a 
decided tendency to darker colors, such as has been noted also 
among British moths. In spite of this tendency, however, some 
forms are lighter than their relatives, the most conspicuous case 
being the light-tailed British squirrel. In several cases the differ- 
ence noted has in part to do with particular phases; thus the 
squirrel has no dark phase, and the ermine does not turn so white 
in winter. The British red grouse, it will be remembered, is 
peculiar in lacking a white winter phase. Some of these differ- 
ences may be due to the direct effect of the mild and moist 
British climate, and would perhaps disappear in the descendants 
of British animals taken elsewhere. The experiments on birds by 
Beebe are very suggestive in this connection. In other cases, the 
distinctions are such as might readily result from changes in one 
or two ** units," such as are observed in experimental breeding. 
"When we have a variable type, subject to losses and new combi- 
nations of unit characters, it is perhaps to be expected that 
different groups of individuals, isolated from one another, will 
after a time produce different homozygous combinations. That 
is to say, the result comes from a long series of ** accidents," 
which will probably not be duplicated in two different places. In 
this way mere isolation may be an adequate cause of modification, 
providing always that through variation degrees of hetero- 
zygosity have arisen. 

In the common house mouse, Mus musculus, Hagedoom^ has 
isolated and figured a great number of color varieties, for nearly 
all of which he bas constructed zygotic formulae. Little* has 
also described and figured a similar series of varieties, appar- 
ently in ignorance of Hagedporn 's paper, which he does not cite. 
He gives zygotic formulae for thirty-two different varieties, but 
not all of them are visibly different. Albino varieties, resulting 
from the dropping out of a particular determiner, may be pro- 
duced, corresponding in other respects to each of the thirty-two 
colored forms, although they all look alike, and will only show 
their true characters on crossing. Several of the varieties show 

1 Zeii. f. ind, Ahst. Ver,, 1912. 

'"Experimental Studies of the Inheritance of Color in Mice," 1913. 



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No. 567] SHORTER ARTICLES AND CORRESPONDENCE 179 

noteworthy fluctuating variability, due to differences in ex- 
pression. 

Muts musculus, then, is very conspicuously variable in color; 
yet Miller's book records only one subspecies, that of the Medi- 
terranean region and the Azores, which is less dusky and more 
yeUowish, with the under parts buffy grayish. It possibly agrees 
with Little's ** dilute black agouti" variety. On the other hand, 
M. musculus has a recognized subspecies in Mexico, whete it 
must have developed since the species was introduced by man. 
The mice of St. Eilda and the Faroe Islands, although given as 
distinct species, are derivatives of Mus musculus, differing in 
other points than color. In connection with subspecific differ- 
ences in size, Sumner's experiments with different temperatures 
should be noted, since they prove that differences of temperature 
might lead to readily measurable differences in dimensions, 
wholly unconnected with losses of determiners or new zygotic 
combinations. Whether or not diverse conditions of this sort 
would ultimately affect the germ plasm, their effects would be 
patent long before and quite independently of any such modifi- 
cation. On the whole, the poverty of Mu^ muscuiu^ in subspecies 
would suggest that the variations observed by breeders are not, 
as a rule, the stuff that new subspecies are made of. Against this 
argument may well be adduced the fa6t that M. musculus is an 
urban animal, constantly traveling about, so that incipient races 
do not remain isolated. Here the closely related rats, Epimys, 
are worth considering. For Europe Miller can only recognize 
the Norway, Black and Alexandrian rats, all widespread, prac- 
tically cosmopolitan. Yet in the Malay Archipelago, where 
Epimys is distributed over myriads of islands, large and small, 
the species are innumerable. One can almost take a map and 
indicate where new species of Epimys are to be found, namely, on 
those islands still unexplored. Years ago, when the writer was 
actively engaged in studying the British MoUusca and Lepi- 
doptera, the question of endemic forms was constantly in mind ; 
but in those days we failed to discriminate properly between the 
different classes of "varieties. ' ' We made the mistake of looking 
for well-marked ''sports" or aberrations, rather than for con- 
stant but only slightly distinguished local races. There was a 
practical reason for this, in the fact that by searching the litera- 
tore we could ascertain whether a well-marked variation had 
been reported from the continent ; whereas the determination of 
subspecific types analogous to those described by Miller among 



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130 THE AMEBIC AN NATURALIST [VouXLVm 

mammals required long series from different parts of Eiirope, 
and these we did not possess, and could not readily obtain. Miller, 
following the custom of mammalogists, lays great stress on sub- 
species, but almost ignores individual variations, except such as 
are expressed by the statistical data regarding size. By reading 
the synonymy, one can see that many such variations have re- 
ceived names, and I can not doubt that the time will come when 
iheOd names will be generally used. In this case, it will be 
extremely desirable to use the same adjectival name for analogous 
varieties of different species, and beyond the limits of subspecies 
it ought not to be held that a name once used in a genus can not 
be employed again. It may be true that most or all of the '* indi- 
vidual" varieties can be expressed by zygotic formulae, but one 
can not remember all these formulae, nor use them in speech with 
any comfort. Moreover, they have to do with the germinal con- 
stitution rather than the patent characters. Little provides all 
his varieties with polynomial English appellations, but would not 
Latin varietal names be better f Following his theory con- 
cerning the pigments, some of the varieties receive names 
which do not suggest the animals at all; thus ''brown-eyed 
yellow," according to the apparently excellent colored plate, 
is light orange-ferruginous, while "sooty-yellow" is dark gray 
with yellowish under parts. Morgan* describes a wild variety of 
M. musctdv^ from Colorado, which he calls ''mauve," but from 
the detailed account it is rather "fauve," namely, fulvous op 
yellowish brown. It must be similar to the Old World subspecies 
azoricUs, or possibly that subspecies introduced t If we had 
standard scientific names for the different forms, we should try 
to compare our specimens with the types or descriptions of those 
names, and it would not be left to authors to use such miscellane- 
ous descriptive terms as might occur to them. For Mus musculus, 
possibly Little's apparently excellent colored plates might be 
made the standards for a series of names. Thus his Fig. 9 
(pi. 8) is the animal named niger as long ago as 1801; Fig. 10, 
the dilute black, would naturally take the name nigrescens. 
Fig. 12 is probably albicans of Billberg, 1827. 

Mammals Peculiab to tbs British Islands 
In$ectivora 
8orex aranem castaneus (Jenyns 1838). Great Britain. Not so dark as true 
araneuB, 

tAnn, N, T. Acad, 8ci., XXT, p. 106. 



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No. 567] 8H0BTEB ARTICLES AND COBBESPONDENCE ISi 

Borex granti (Barrett-HamUton and Hinton 1918). Inner Hebrides. Dif* 
fera from araneus bj the eontraat between bright-colored flanks and 
dusky npper parts; teeih also different. 

Veamys fodiens hicohr (Shaw 1791). Qreat Britain. Under parts nsoally 
washed witit wood-brown instead of bnffy whitish; skull smaller. 

Chiroptera 

Khwolaphus ferrum-equinum insulanuB Barrett-Hamilton 1910. Central and 
8. England. Wing shorter. 

MMnolophui hippasideros tninutiu (Montagu 1808). England and Ireland. 
Wing shorter. 

Camivora 

Musiela erminea stabUis (Barrett-Hamilton 1904). Mainland of Great 
Britain. Bather large, with large teeth; color somewhat different, a 
little darker above. Change to white in winter less complete and regu- 
lar than in continental forms. 

Miuiela erminea riciruB (Miller 1907). Islands of Islay and Jura, Scot- 
land. Smaller than etdbiUa; proportions of skull different. 

Mustela hibemica (Thomas and Barrett-Hamilton 1895). Ireland and Isle 
of Man. Quite distinct; recognized by combination of black-tipped, 
heavily penciled tail with entirely dark ear and upper lip. Superficially 
like certain North American forms. 

Felia sylvestria grampia (Miller 1907). Scotland; formerly throughout 
Great Britain. Darker, with more pronounced black markings. 

Bodentia 
Lepus europcBus occidenialis de Winton 1898. England, Scotland and Isle 

of Man. Buffy tints rich and dark. 
Lepus iimidus scotieus (Hilzheimer 1906). Highlands of Scotland. 

Smaller; rarely becomes so white in winter as Alpine race. 
Lepus T^emicus Bell 1837. Ireland. Distinguished by the strongly russet 

color and partial or complete absence of white winter coat. Larger than 

seoticus. 
Bvotomys aistoni Barrett-fiamilton and Hinton 1913. Island of Mull, 

Hebrides. 
Evotomys glareolw hritannicus (Miller 1900). Great Britain. Smaller; 

color less intense. 
Evotomys skomerensis Barrett-Hamilton 190S. Skomer Island, off coast of 

Wales. Color nbove unusually light and bright; skull peculiar. 
Microtus agrestis esBsul Miller 1908. North and South Uist, Hebrides. Be- 

sembles true agrestis of Scandinavia; teeth peculiar, a character usually 

present which elsewhere in the species occurs as a rather rare anomaly. 
Mierotus agrestis maegiUivraii Barrett-Hamflton and Hinton 1913. Island 

of Islay, Hebrides. 
Mierotus agrestis Iwrtus (Bellamy 1889). England and South Scotland. 

Smaller than typical agrestis; upper parts noticeably tinged with rus- 
set, and venter washed with wood-brown. 
Mierotus agrestis negleotua (Jenyns 1841). Highlands of Scotland. Not 

so small as Mrtus; upper parts darker. 



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182 THE AMERICAN NATURALIST [Vol. XL VIII 

Miorotus orcadenm Millais 1904. South Orkney Islands. Belated to If. 
aamius of Guernsey and the Pleistocene M, corneri of South England. 
Distinguished by its large size and dark color. 

Miorotus sandayensis (Millais 1905). Sanday Island, N. Orkney group. 
Allied to orcadensis, but skull differing; upper parts much lighter. 

Miorotus sandayensis westrcB MiUer 1908. Westray Island, N. Orkney group. 
Not 80 pale as in typical form; teeth differing a little. * 

Arvioola amphilius (L. 1758). Typical subspecies. England and South 
Scotland. Large; color moderately dark. 

Arvioola amphibius ater (Macgillivray 1832) = reta Miller 1910. Scot- 
land, except southward. Darker, melanism frequent. The name was 
changed on account of EypudoBus terrestris var. ater Billberg 1827, but 
the change is perhaps needless, as Billberg 's animal was not a sub- 
species, and has not been treated as a species or subspecies under 
Arvioola. 

Apodemus hehridensis (de Win ton 1895). Lewis and Barra islands, Hebri- 
des. Large, with small ears; color dark. 

Apodemus hirtensis (Barrett-Hamilton 1899). Island of St. Kilda. Near 
hehridensis, but skull larger and color darker. 

Apodemus fridariensis (Kinnear 1906). Fair Isle, Shetland group. Large; 
skull peculiar; colors also somewhat peculiar. 

Apodemus fia/vioollis wintoni (Barrett-Hamilton 1900). England. Under 
parts with duller color, pectoral spot more diffuse. 

Mus muralis Barrett-Hamilton 1899. Island of St. Kilda. Like M, musoulus 
but feet and tail less slender; skull peculiar. 

Mus fceroensis (Clarke 1904). Faroe Islands. Larger than musoulus and 
muralis; hind foot very robust; tail thickened. 

Sciurus vulgaris leuoourus Kerr 1792. Great Britain and Ireland. Small; 
tail drab, fading in summer to cream buff. No dark phase. 

Vngulata 

Cervus elaphus sootious Lonnberg 1906. Great Britain. Color darker and 

less gray than in the related Norwegian form. 
Capreolus oapreolus thotti Lonnberg 1910. Great Britain. Darker, face 

darker than body. 

I thought it of interest to compare the above British list with 
a similar one for the Spanish peninsula (Spain and Portugal). 
The latter area is continuous northward with France, but the 
Pyrenees constitute a barrier. The Iberian peninsula differs so 
much in its recent geological history from Britain, and is at the 
same time so much more southern, that we should expect to find 
the faunal elements very different. This expectation is realized, 
yet the difference in numbers between the two lists is not very 
great, and the number of Iberian forms treated as distinct 
species is exactly the same (12) as that for the British Islands. 
This suprising result is evidently due to the numerous small 



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No. 567] SHOETEB ARTICLES AND CORRESPONDENCE 183 

islands of the British group, sti<;h islands being wanting around 
the coasts of Spain. 



Mammals Peculiab to thx 
Inseetivora 
Talpa ocoidentaUs (Cabr.). 
Oalemys pyrenaious rufulus 

(GraeDs.). 
8<fr€x araneus granariut Miller. 
Neomys anomalus Cabr. 
Crocidura mimuJa cantabra (Cabr.). 
Crocidura russula dnira MiUer. 
Brinaceus europcBus hispanioua B.- 

Ham. 



Chiroptera 



(None.) 



Camivora 
Cants lupu8 signatus Cabr. 
Cants luptu deiianvs Cabr. 
Meles metes marianensis (Graells.). 
Maries foina mediterranea 

(B.-Ham.). 
Mnstela nivalis iberica (B.-Haiii.). 

(Also Balearic Is.). 
Mustelaputoriusaureolus (B.-Ham.). 
Mungos toiddringtonii (Gray). 
Oenetta genetta (L.), typical nibsp. 
Felts sylvestris tartessia (Miller). 
Lynx pardeUus Miller. 

Bodeniia 
Lepus granatensis Bosenb. 

(Also Balearic Is.). 
Leptu granatensis galUseius Miller. 

Univebsity of Colokado 



Spanish (Iberian) Pininstjla 
Eliomys lusitanieus (Beuvens). 
Glis glis pyrenaious Cabr. 
Microttu agrestis rosianus (Bocage). 
Mieroius asturianus Miller. 
Arvicola sapidtu Miller, typical 

subsp. 
Pitymys lusitanieus (Gerbe). 
Pitymys maruB (Major). 
Pitymys pelandoMus Miller. 
Pitymys depressus Miller. 
Pitymys iberious (Gerbe), typical 

sabsp. 
Pitymys iberious centralis Miller. 
Pitymys iberious pasouus Miller. 
Pitymys iberictu regulus Miller. 
Mus spicilegus i kfanicus Miller. 
Mus spicUegtu hispanicus Miller. 
Soiurtu vtUgaris numantius MiUer. 
Soiunu VtUgaris infusoatus (Oabr.). 
Sdmus VtUgaris segura Miller. 
Sciurus vulgaris bcsticus (Cabr.). 

UngtUata 
Bus sorofa castUianus Thomas^ 
8us sorofa bcetious Thomas. 
Cervus elaphus Mspanieus Hilxh. 
Capreolus oapreohu oantu Miller. 
Capra pyrenaica lusitanica (Franca). 
Capra pyrenaioa victoria Cabr. 
Capra pyrenaica hispanioa (Schimp.). 
Bupicapra parva (Cabr.). 

T. D. A. COCEERELL 



LITEBATUBE CITED 
BatesoB, W. Mendel's Principles of Heredity Cambridge (England) 

University Press. 1909. 396 pp. 
Castle, W. E. Heredity of Coat Characters in Guinea-pigs and Babbits. 

PubL Carnegie Inst of Wash. No. 23, 1905. 
Cannot, L. La loi de Mendel et I'h^r^dit^ de la pigmentation chez les 

souns. 4me note. Arch, Zool exp. et g4n. Notes et Bevue, 1905. 
Darbishire, A. D. Notes on the Besults of Crossing Japanese Waltzing 

Mice with European Albino Baees. Biometriica, Vol. 2, p. 101, 1902. 



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184 THE AMERICAN NATURALIST [VouXLVHl 

Poncsster, L. On the Inheritance of Coat Colour in Bate. Proo, Camb, 
Phil. Soc, Vol. 12, pt 4, p. 215, 1905. 

Durham, F. M. A Preliminary Account of the Inheritance of Coat Colors 
in Mice. Bept. Evol. C't'ee. B07. Soc., IV, 1908. 

Hagedoorn, A. L. The Genetic Factors in the Development of the House- 
mouse which Influence the Coat Color, with Notes on Such Factors in 
the Development of Other Bodents. Zeit fur indukt, Abst. u. Vererh,, 
Bd. 6, pp. 97-136, 1912. 

McCurdj, H., and Castle, W. E. Selection and Crossbreeding in Belation to 
the Inheritance of Coat-pigments and Coat-patterns in Bats and Mice. 
Publ. Carnegie Inst, of Wash., No. 70, 1907. 

Morgan, T. H. Becent Experiments on the Inheritance of Coat Color in 
Mice. Am. Nat., Vol. 43, pp. 494-510, 1909. 



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NOTES AND LITERATURE 

SWINGLE^ ON VARIATION IN F^ CITRUS HYBRIDS 
AND THE THEORY OP ZYGOTAXIS 

SwiKGiiB in two recent papers has published some very inter- 
esting observations on Citrus species and their F^ hybrids. On 
the basis of these observations, the somewhat startling statement 
is tnade that current theories of heredity and variation give no 
adequate explanation of variability in F^ hybrid generations 
from ''pure bred'' parent strains. Swingle assumes this vari- 
ability to be so great that qualitative differences in chromosomes 
can not account for it. As the chromosomes in the F^ hybrid 
remain unfused until synapsis, there is said to be no opportunity 
for quantitative exchange of hereditary substance, so that this 
variation can not be accounted for on this basis. Hence, 

if proof can be given to show that in certain specific cases, pairs of 
gametes of identical hereditary composition* give rise to very diverse 
organisms, the way has been opened for a general reinvestigation of the 
validity of our modem theories of heredity. 

The term "pure bred" as used by Swingle implies that cer- 
tain Citrus species reproduce themselves in a relatively faithful 
manner from seed, there being no overlapping of distinguishing 
specific characters and very little variation of these characters 
intraspecifically. C. aurantium and C. trifoliata are examples 
of such widely separated species. The former has been grown 
from seed in Florida for two hundred years, and though varia- 
tions have appeared, they are said to differ but little from the 
general type of C. a/urantium, and in no way to approximate 
that of C. trifoliata. 

On the basis of evidence of this kind, Swingle believes the 
various Citrus species (C aurantiuniy C. trifoliata, C. medica 
limonum, etc.) breed true in nearly all their characters and 
especially in those which differentiate them from one another. 
Hence, for genetic studies, the germ cells of these species are 

1 Swingle, W. T^ "VariAtion in First Oentration Hybrids (Imperfect 
Domisanoe) : Its Possible Explanation through Zjgotaxis,'' IV® Conf. In- 
temat. de Genetique^ Paris, 1911, pp. 381-394; <<Some New Citrus Fruits," 
Amer. Breed. Ma^,, 4: 83-95, 1913. 

s The italics are mj own. 

185 



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186 THE AMERICAN NATURALIST [VouXLVni 

assumed, in respect to these diflFerential characters, to be pure; 
or, expressed in more technical language, each species is for the 
characters under observation, genotypically homozygous. This 
assumption is based on wholly inadequate evidence, as will be 
shown later. 

Citrus trifoliata crossed with other Citrus species (C auran- 
tium, etc.) gave Fj hybrid families showing a large degree of 
variability, even when the seeds from a single cross having 
identical male and female parents were grown. This variability 
expressed itself in foliage, habit of growth, and fruit, and was 
especially noticeable in the latter, the fruits of the Fj individuals 
showing differences in color, size, texture, shape, number of seeds, 
and flavor. For example, from a single cross of C. trifoliata X C. 
aurantium, the 11 resulting hybrid seeds gave rise to Fj plants 
(citranges) differing in foliage, habit of growth, and very strik- 
ingly in fruit. The fruit of one of these citranges, the "Morton," 
was smooth, round, very large, and orange-colored ; those of the 
**Colman" were rather flattened, globose, pubescent, yellow, al- 
most seedless, and lacked the disagreeable oil common to the 
others; while those of still another type, the ** Willi ts," were 
often monstrously fingered. The ** Phelps" was bitter, while the 
''Saunders" almost lacked this quality. The "Rustic" often has 
double fruits with many seeds, and a habit of growth more like 
its aurantium parent. 

When varieties of the lemon were crossed with C. trifoliata, 
still greater differences in the F, generation (citremons) resulted. 
These consisted largely of "abnormal" foliage developments. 
Hypophylls, though absent in the common Citrus species are ex- 
tremely characteristic of C. trifoliata. About 20 per cent, of the 
lesnon-trifoliata hybridis developed an intensified form of this 
character, and this proportion occurred in each case in crosses 
involving three different varieties of lemon. The tangerine 
orange X grape fruit (tangelo) in the F^ generation was almost 
as variable as the citrange families. Fj hybrids between the 
West Indian lime and the kumquat (limequat) were strikingly 
different in such characters as aroma, flavor, acidity of pulp and 
thickness of skin. 

Although much stress has been laid on the differences in these 
Fi hybrids, there were numerous similarities. For example, all 
the Citrus hybrids involving C. trifoliata in their parentage have 
compound, semi-evergreen leaves, increased hardiness and fruits 



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No. 567] SHORTER ARTICLES AND CORRESPONDENCE 187 



with abundant bitterish, acid juice. Two of the citranges (Col- 
man and Cunningham) have the pubescent fruit character of 
C. trifoliata, while the others are smooth-skinned. 

The author's data led him to formulate in substance the follow- 
ing conclusions, which I have grouped and stated in my own 
language. 

1. Citrus species are but slightly variable in the characters 
which diflferentiate them, and, in the sense that no overlapping 
takes place, may be said to breed true, their germ cells being 
genetically pure for these differential characters. 

2. Individual plants of the Fj hybrid generations between these 
species are strikingly variable, although all are, in a given cross, 
the zygotic product of pairs of gametes of ** identical hereditary 
composition." 

3. Modern theories of heredity can not account for this varia- 
tion. 

These are not the conclusions, however, in which all present- 
day geneticists would! concur. In the first place, few ''modem" 
geneticists would take Swingle's view concerning the **pure 
breeding" ability of the various Citrus species, nor even of C. 
aurantium. Webber, in the Encyclopedia of American Horti- 
culture, notes that 70 varieties of the common sweet orange are 
grown within our borders, and although a few varieties are 
fairly constant, the majority of these do not breed true from seed. 
Practically the same idea has been gained by certain prominent 
taxonomists of the genus Citrus. De CandoUe specifically calls 
attention to the remarkable variability of the whole group ; and 
Professor Hume of Florida remarks on the same fact in certain 
Experiment Station publications. As to the variability among 
the individuals in the special strains used by Swingle in his breed- 
ing work, no data are given, so that it can not be afSrmed that 
inbred progeny from them would have been duplicates as far as 
hereditary characters are concerned. Citrus plants naturally 
cross fertilize, and from this cause alone no dependence can be 
placed on their ability to produce progeny, which are exact dupli- 
cates of themselves when inbred; in fact, the inference is that 
they would not. Hence, as far as intraspecific constancy of 
hereditary characters is concerned. Swingle's statement can not 
be accepted until more exact information is produced. 

Swingle says no interspecific gradations occur between these 
various species, especially C. trifoliaia and C. aurantium. Qrant- 



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188 THE AMERICAN NATURALIST [Vol. XLVUI 

ing this, the two species have clearcut differences in leaves (ever- 
green or deciduous, unifoliolate or compound), in resistance to 
cold (difference in ability to withstand certain degrees of tem- 
perature) and in numerous fruit characters (presence or absence 
of pubescence, quality of juice, quantity of seed, size of fruit, 
etc.). 

From the standpoint of modem theories of heredity as regards 
variation in Pi hybrid generations, it matters little whether so- 
called species intergrade or whether their differences are clear-cut 
and all variation is intraspecific. In either case, if crosses were 
made, variation among the F^ individuals from a single family 
might or might not occur. In either case, no violence to modem 
theories of heredity would result and no new problems would 
arise. But if two species that differ from each other in part or 
all of their characters, but breed true intra-specifically (geno- 
typically homozygous) are crossed, and Fi variation results, then 
modem theories of heredity would be compelled to change front 
and invoke the aid of new hypotheses. Swingle's data, assuming 
that intraspecific variation in Citrus species occurs, does not 
present a problem of this kind at all. C. aurantium and C. tri- 
foliatu each possess distinctive characters, but convincing data are 
not at hand to warrant any belief in the homozygosity of these 
differential eharacters or of even those the two species may have 
in common. The evidence directly, and one might almost say 
conclusively, opposes such a conclusion. If these species are not 
homozygous in all of their characters, then one can not affirm, in 
the light of modem theories, that all the gametes produced by a 
particular group of individuals called a species are identical in 
hereditary composition, nor even that the gametes of one indi- 
vidual of such a species are identical as to hereditary potenti- 
alities. At the risk of wasting valuable space by repeating what 
is extremely common knowledge to genetic students, let us assume, 
for the purpose of argument, that C. (mrantium and C. irifolicUa 
are homozygous in all their respective characters except one. In 
the former, the character A is heterozygous and peculiar to this 
species. Likewise, in C, trifoUata, B is heterozygous and differ- 
ential. All the remaining^ characters of the two species may be 
symbolized, respectively, by the formulaB XX and TT. When 
XXAabb (C. aurantium) is crossed with YYaaBd (C. trifoltata)^ 
the resulting progeny would appear in the approximate propor- 
tion of 1 XYAaBb : 1 XYAabl : 1 XYaaBb : IXYaabb, providing 



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No. 567] NOTES AND LITEBATURE 189 

A and B are single factor characters. In the majority of char- 
acters, the Fi hybrids would be intermediate or possess those of 
either one or the other parent, since all the F^ individuals would 
be alike as far as any hereditary quality symbolized by XY is con- 
cerned, providing the plants were all grown under the same en- 
vironmental conditions. But these F^ individuals would not be 
alike as regards the inheritance of the characters A and B. Ex- 
perimental evidence from crosses of this kind show us that four 
different Fj forms may result, the distinctions between them aris- 
ing from the presence or absence, through inheritance, of the 
characters A and B. Dominance is assumed to be absent in this 
illustration. 

Swingle's Citrus hybrids, though involving greater complexity 
because a large number of parental characters instead of two are 
probably heterozygous, are of the same general type as those of 
the illustration and lend themselves to the same interpretation. 
Owing to the absence of sufficient exact experimental data, one 
can not speak of unit characters and factors in these hybrids, but 
one may say without violence to modem theories of heredity that 
one or both of the parents involved in the crosses which produced 
the Colman and the Cunningham were heterozygous in the factors 
or factor for pubescence, that various size factors were hetero- 
zygous and that one parent was homozygous for absence and one 
for presence of the factors for hardiness, compound leaves and 
evergreen foliage. 

Fi variation in Citrus hybrids then, in the light of the data at 
hand, apparently results from differences in the gametic compo- 
sition of the heterozygous parents. 

Swingle calls attention to other cases of variation in F^ hy- 
brids from two pure stocks which support his contention that this 
phenomenon of Fi variation is very general, though usually 
obscured through variation due to heterozygous parent stock. 
CoUins and Kempton* crossed a race of com breeding true to 
waxy endosperm with one constant for homy endosperm. Homy 
endosperm was dominant in F^ and the Fj generation segregated 
in the expected ratio of 1 waxy to 3 homy kemels. This ratio 
represented the average proportion of each when the ears of all 
the plants were lumped together. The F, progeny of each selfed 

tColHos, G. N., and Kempton, J., n, 1912, ''Inheritance of Waxy Endo- 
spenn in Hybrids of Ohinese Corn,'' IV** Conf. Internal, de Genetique, 1911, 
p. 34T; alto Cir«. No. 120, Bur. of P. I., V. 8. Dept of Agr., 1913. 



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190 THE AMERICAN NATURALIST [Vol. XLVHI 

Fj plant when taken by itself gave some ears as low as 13.7 per 
cent, waxy, while others exceeded the expected proportions and 
gave ears as high as 33.3 per cent. waxy. The investigators point 
out that this variation is not the result of the laws of chance as 
the deviation is far greater in many cases than the probable error. 
Therefore, says Swingle, 

there can be no doubt but that their varying percentages represented 
real differences in the hereditary composition of the first generation 
plants. It would be hard to find a more conclusive case since there could 
be no doubt as to the purity of the parents and what is more rare no 
possible doubt as to whether a given kernel had a waxy or a homy 
endosperm. 

Mendelians are said to be unaware how fatal this phenomena is 
to some of the chief tenets of modem theories of heredity, and 
they are also accused, somewhat unjustly, I believe, of applying 
the term ''imperfect dominance" to this and to the Citrus 
phenomena. 

In this case, both parents were undoubtedly homozygous for 
their respective endosperm characters, so that heterozygosity will 
not account satisfactorily for the deviations. But this is a dif- 
ferent phenomena than Swingle found in his Citrus hybrids, for 
here one is dealing with a fluctuation in a proportion or ratio 
involving the same character, while in his experiments the diffi- 
culty was the variation in presence and absence of distinct and 
often new characters, indicating an extremely heterozygous 
parentage. 

As an explanation or working hypothesis for his own and 
similar data. Swingle advances a somewhat new and suggestive 
chromosome theory on the assumption that it fills an urgent need. 
The theory of zygotaxis, as it is called, may be summarized as 
follows : 

Maternal and paternal chromosomes probably persist side by 
side in the cells, unchanged in quality and number throughout 
the whole development of the F^ organism. This being true, 
Swingle, in order to explain his data, assumes that the influence 
in character formation exerted by chromosomes on the F^ hybrids, 
is in some cases due to their relative positions in the nucleus, and 
that these relative positions result from accident or at least are 
determined at the moment of nuclear fusion in fertilization, and 
remain unchanged in succeeding cell generations. He further 



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No. 567] NOTES AND LITERATURE 191 

assumes that those chromosomes lying nearest the nuclear wall 
(peripheral) are better nourished than those centrally located, 
and hence they exert more influence in character formation, and 
dominating synapsis, produce gametes similar in their hereditary 
character to the cells of the first generation hybrids, whose char- 
acter in turn was determined at fertilization by the configuration 
the chromosomes took in the fusion nucleus. On this theory, 
reversions, sports, etc., may result from sudden changes in the 
nuclear configuration. 

Three types of nuclear configuration are assumed to occur in 
higher organisms, the character and effects of which are synop- 
tically outlined below. 

1. Interspecific Hybrids, — ^Usually sterile and intermediate. 
Chromosomes repel each other and occupy opposite sides of the 
Pi zygote nuclei, exerting equal influence in the ontogeny of P, 
organisms, explaining why first generation hybrids of this char- 
acter are always intermediate, little variable and usually sterile. 
Synapsis often impossible. 

2. Mendelian Crosses, — Abnormally inbred races of domesti- 
cated animals and plants. Pj generation usually intermediate, 
fertile, dialytic at synapsis. Dominance of certain characters in 
these hybrids is due to the inherited potentialities of the chromo- 
somes rather than to their nuclear positions. 

3. Normal Cross-bred Species, — ^Probably normal in wild 
species. Hybrids usually vigorous, fertile, and variable. Pree 
intermingling of chromosomes in the fusion nucleus at fertiliza- 
tion. Nuclear configuration permanent for each individual. 
Synapsis normal. 

This elaborate and attractive theory, based admittedly to a 
great degree on assumptions, is advanced by Swingle in the belief 
that it will help to clarify the problems of heredity, even though 
he acknowledges it does not help one to arrive at satisfactory 
explanations. In the reviewer's opinion, however, the field of 
genetics is already burdened with enough theories of this par- 
ticular type and the somewhat unnecessary but ever-increasing 
new additions serve to confuse rather than clarify the ideas of 
the average student of genetics. Besides, Swingle's assumption 
that maternal and paternal chromosomes in the cells of Pj hybrids 
repel each other and do not mingle in the Pi zygote cells is not 
borne out by the few cytological facts at our command. Rosen- 



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192 THE AMERICAN NATURALIST [Vol. XLVHI 

berg V work on species hybrids of Drosera, Moeukhaus V investi- 
gations of species hybricEs in fish and some work on certain 
hybrids in the Echinodermata group give us facts that directly 
oppose such an assumption. As a further criticism^ one may say 
that most biologists who have had experience with pedigree cul- 
tures would decidedly criticize the synoptic outline and the nar- 
row sphere assigned to Mendelian phenomena. 

Aside from the theoretical considerations, these two papers con- 
tain djescriptions of CiirusAike species new to occidental horti- 
culture, together with a somewhat detailed account of the various 
Citrus hybrids and their hardiness and practical value, showing 
the truly fine results achieved by the workers in this field toward 
moving the Citrus belt northward and adding new varieties of 
this genus to the world's horticulture. 

Obland E. White 

Bbookltn Botanic Oabden^ 
December 4, 1913 

>Bosenberg, O., " Qytologische und Morphologische Studien an Drotera 
Umgifolia X D. rotundifolia," Kungl. Svenska VetenskapBakademiens Hand- 
linger., 43, N: on, pp. 1-64, 1909. 4 Tafn. 

«Moenkliau8, W. J., "The Development of the Hybrids between Fwtduhu 
heteroclitua and Menidia notaia with especial reference to the B^avior of 
the Maternal and Paternal Chromatin," Amer, Jour, of Anatomy, 3: 29-65, 
1904. Plates I-IV. 



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THE 

AMERICAN NATURALIST 

Vol. XLVIII April, 29U No. 568 

THE ORIGIN OF X CAPSELLA BURSA-PASTOEIS 
ARACHNOIDEA 

DR. HENRI HUS 

University op Michigan 

Since Jordan^ described a number of elementary spe- 
cies of Capsella Bursa-pastoris, their constancy has been 
a subject of cultural experiment. Herbarium material 
demonstrates the existence of numerous apparently imde- 
scribed forms. The finding of strikingly distinct forms, 
such as Capsella Heegeri^ and, more recently, C. Viguieri,^ 
the work of Almquist* and that of ShuU have added to 
the interest which this species holds for the investigator. 
It was ShuU who determined the zygotic constitution of 
various forms. To be able to demonstrate this with ex- 
actitude is of the greatest value since Bateson and Lotsy 
expressed their doubt as to the homozygocity of deVries's 
(Enothera Lamarckiana. It was left to Nilsson^ to clearly 
show its necessarily heterozygous character. The inter- 
est aroused by this paper® leads me to believe that an 

1 Jordan, A., ' ^ Diagnoses d 'esp^ces nouvelles ou m^connues pour servir 
de mat^riaux k une ilore r^form^e de la France et des contr^s voisines." 
Paris, 1864. 

2 Solms-Laubach, H. Graf zu, ''Craciferen studien. I. Capsella heegeri, 
eine nenentstandene Form der deutschen Flora/' Bot, Zeit., 55: 167, pL 
7, 1900. 

8 Blaringhem, L., ''Les transformations brusques des §tres vivants." 
Paris, 1911. 

^Almquist, E., "Studien fiber die Capsella Bursa-pastoris (L.)," Ada 
Horii Bergiani, 4: No. 6, 1907. 

s Heribert-Nilsson, N., * ' Die Variabilitat der (Enothera Lamarckiana und 
dai Problem der Mutation," Zeitschr. /. ind, Abst, u. Vererb,, 8: 89, 1912. 

• Lotsy, J. P., ' * Fortschritte unserer Anschauungen fiber Deszendenz seit 
Darwin und der jetzige Btandpunkt der Frage," Progressus Bei BotaniccB, 
4:361,1913. 

198 



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194 THE AMERICAN NATURALIST [Vol. XLVUI 

account of certain cultures of Capsella, in which muta- 
tions were simulated, would be of timely interest. 

During the winter of 1908-1909, I collected in a green- 
house at Ann Arbor, Michigan, and at the disposal of the 
Botanical Department of the University of Michigan, 
twelve rosets of Capsella Bursa-pastoris, the leaves of 
whic'h showed certain more or less striking morphological 
differences. With the hope of isolating certain biotypes, 
the rosets were placed in pots and permitted to flower. 
No measures were taken to prevent the accidental trans- 
ference of pollen, but the pots were placed about six 
inches apart. This, as will be shown later, is the only 
precaution necessary to guard against cross-pollination, 
provided the cultures are carried on in a greenhouse and 
during the winter months. After a portion of the seed 
had ripened, the plants, the majority of which retained 
their climax leaves, became herbarium specimens. More 
recently, after constant association has enabled me to 
detect minute differences, it has been possible to identify 
some of these plants with two of the biotypes described 
by ShuU,^ to wit, rhomhoidea and simplex. At the time 
of collection, the differences were sensed, but could not be 
described technically, since the extent of the influence 
wielded by fluctuating variability was an unknown quan- 
tity. Never before had I so fully realized the truth of de 
Vries's statement.® 

We are trained to the appreciation of the differentiating marks of 
systematic species. . . . Our minds are turned from the delicately 
shaded features which differentiate elementary species. 

The seed obtained was sown in sterilized soil during 
the spring of 1910. From each seedpan 60 individuals 
were transplanted to flats. As the plants grew older, it 
was found that, with a single exception, the seedlings in 
each of the flats were uniform, but that the seedlings in 
the different flats were not alike, three types being dis- 
tinguishable. The interest in these types, for the isola- 

TShull, G. H., ** Bursa huraa-pastoris and Bursa Heegeri: Biot.ypes and 
Hybrids,'' Publ. No. 112, Carnegie Institution of Washington, 1909. 
8 de Vries, Hugo, *' Species and Varieties,'' 689, 1905. 



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No. 568] X CAP SELLA BUBSA-PASTORIS ARACHNOIDEA 196 

tion of which these cultures had been undertaken, soon 
was overshadowed by the behavior of the seedlings bear- 
ing the number 4,108.6 and which were the offspring 
yielded by a plant of a type not described by Shull and 
which I have named X Capsella Bursa-pastoris Setchelli- 
ana, in honor of Professor William Albert Setchell. 



Fio. 1. Appearance op a Linear-leaved Form among Seedlings op Capsella 

Bursa-pastoHs. 

During the time that the seedlings remained in the seed- 
pan, no deviations from the expected course of develop- 
ment were noted. However, after the seedlings had been 
transplanted to flats and had remained there a week or 
so, it became evident that some of the seedlings were not 
making the expected growth. Their development ap- 
peared most insignificant compared with that of the 
majority. A closer examination showed the cotyledons 
to be somewhat larger than normal and the leaves proper 
to be exceedingly small and almost linear. Nor did they 
attain the same length as the leaves of the rosets belong- 
ing to other types. 



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196 THE AMERICAN NATURALIST [Vol. XLVIII 

An explanation of this peculiar development was songht 
in a possible attack on the part of either fungi or bacteria 
or in soil conditions. But the latter were uniform for the 
entire flat. Neither fungi nor bacteria could be demon- 
strated nor did the underground portion of the '* ab- 
normal" plants look imhealthy or underdeveloped. 



Fig. 2. Seedlixus ok x C. . . . SctcheUi and x C. , . . arachnoidef 

At this stage the flat presented the appearance shown 
in Fig. 1. At the time but three types were distinguished, 
the first of these constituted by plants which showed an 
incision of the blade, the second composed of those which 
apparently had entire leaves, and a third, comprising the 
small and linear-leaved rosets, which, because of the spider- 
like appearance of the latter, has been designated xCap- 
sella Bur sa-past oris arachnoidea. There also appeared a 



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No. 568] X CAP8ELLA BURSA-F AST ORIS ARACHNOIDEA 197 

single individual which, while closely resembling the form 
arachnoidea, differed from it in having somewhat spatu- 
late leaves. This plant, a plant of arachnoidea and two 
of Setchelliana, are shown in Fig. 2. 

After photographs had been taken, the plants were 
potted and placed in the frames. None of the plants 
made a growth as vigorous as that of the Capsellas grow- 
ing in the open. The plants of the form arachnoidea de- 
veloped leaves with a greatest length of 15 mm. and a 
greatest width of a little over 1 mm., causing the plant to 
retain its spider-like appearance. The roset with spatu- 
late leaves appeared somewhat more vigorous, the aver- 
age leaf measuring 22 mm. in length, with a greatest width 
of 2.5 mm. In later generations I have been able to ob- 
tain rosets of arachnoidea with a greatest leaf-length of 
100 mm. and a greatest width of 6 mm. 

In the frames, flowering shoots made their appearance, 
those on arachnoidea being remarkable chiefly because of 
their small size, reaching a length not exceeding 12 cm. 
The flowers were small but well-formed. No well-devel- 
oped pollen could be demonstrated. Seed did not form 
and the capsules retained their original form, typical of 
non-fertile capsules in Capsella Bursa-pastoris, remind- 
ing one of the capsules of Capsella Heegeri. They do not 
resemble the fertile capsules of C. procumbens. In the 
next generation I saw a single capsule formed on arach- 
noidea as the result of cross-fertilization, and in this case 
it differed in no manner from the normal capsule such as 
we know it in Capsella Bursa-pastoris. 

The ''normal" plants, i. e., all those not belonging to 
the form arachnoidea, matured a large amount of seed. 
No measures were taken to prevent cross-pollination, but 
no other plant of Capsella Bursa-pastoris, within a radius 
of twenty feet, was in flower. 

At this time, another attempt was made to group the 
plants. It was foimd that the criterion used earlier, i. e., 
the incision of the blade, no longer could be relied upon, 
since plants, which at the time of the previous coimt, had 
shown an entire margin, now were more or less incised. 



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198 THE AMEBIC AN NATURALIST [Vol. XLVIII 

Unfortunately, after the seed had been collected, the plants 
were destroyed, having lost their climax leaves. An attempt 
to group them later with the aid of photographs failed, be- 
cause photographs of all plants were taken during the 
earlier stages only, i. e., before the appearance of the cli- 
max leaves. Another classification, for which climax leaves 
are not . essential, and which is based upon the relative 
width of the first six or eight leaves, yields for 54 plants 
the proportion: ''wide" 31, ''narrow" 16, "linear" 7, the 
ideal proportion, as since worked out, being 33 : 16 : 16. 
The fact that the number for "linear," which represents 
the form arachnoidea, is too small by 9, may be ascribed 
to various circumstances, among others the fact that the 
last row in the flat did not appear in the photograph upon 
which the count was based. It is in the last row of a flat 
one ordinarily meets with the smaller or at least less vig- 
orous individuals and it is very probable that in this last 
row occurred a large percentage of individuals belonging 
to arachnoidea. Furthermore, not all the seedlings, but 
only sixty, were taken in each case. Almost unconsciously 
one selects the largest individuals when transplanting 
from seedpan to flat. It is probable that in this process 
there were eliminated a greater percentage of seedlings 
of the linear form than of any of the others. Hence no 
great weight can be attached to the proportion obtained. 
The collection of seed brought the work for 1910 to a 
close. As far as I was aware, no forms similar to arach- 
noidea had been either noted or described by any one who 
had devoted his time to culture experiments with Cap- 
sella. Neither Shull in America, nor Almquist in Swe- 
den, nor Lotsy® in Holland, has made mention of such 
forms in their publications. The fact that no seed was 
produced by the aberrant form seemed to hold out little 
hope for the continuation of the cultures, and the sole 
trace left by this new form, if taxonomic form it was, 
threatened to consist of but a few photographs and some 
alcohol specimens. A single possibility presented itself. 

»Lotsy, J. P., * * Vorlesungen iiber Deszendenztheorien, ' ' 1: 180, Jena, 
1906. 



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No. 568] X CAPSELLA BURSA-PASTORIS ARACHNOIDEA 199 

Whether the parent plant was of a hybrid character or 
whether the parent plant was mutating, and the new form 
or forms were to be looked upon as mutants, in either 
case there existed the possibility, if not the probability, 
that from the seeds obtained from those plants of the 
second generation which appeared ''normal," a third gen- 
eration might be obtained which would again present the 
abnormal form. Such indeed proved to be the case. 



Fig. 3. Early Stages in the De>*eia>pmext of Broad-i.eaved, Narrow-leaved 

AND Li NEAR- LEAVED FORMS OF Capftcllu. 

The seed for the next generation was obtained from 19 
plants. The seed was sown separately in pots of steril- 
ized soil. Certain of the parent plants, which we now 
identify with ShuU's simplex and rhomboidea, produced 
a uniform, broad-leaved offspring. Others behaved like 
the parent, the form arachnoidea appearing in 197 indi- 
viduals out of a total of 979, which does not include the 
713 which bred true to the broad type. (For an illustra- 
tion of these types see Fig. 3.) 

It is unnecessary to go into details as to the various 
theories which suggested themselves as a solution of the 



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200 THE AMERICAN NATURALIST [Vol. XLVHI 

origin of the linear-leaved form which, becatise of its 
striking appearance, concentrated the attention upon it- 
self. That perhaps we were dealing with a mutation was 
a thought which most naturally obtruded itself upon 
the mind of one who, for years, had fruitlessly tested 
a large number of species in the hope of discovering a 
case analogous to that of (Enothera Lamarchiana}^ The 
possibility of a cross between a local form and either 
Capsella Heegeri or C. procumbens, suggested itself. 
However, the seedling stage of either of these two forms 
does not bear the remotest resemblance to that of Cap- 
sella arachnoidea. At the same time there was slight 
reason for believing that either Capsella Heegeri or Cap- 
sella procumbens ever had been grown in Ann Arbor. 

During 1911 and the greater part of 1912, the problem 
rested here, no satisfactory explanation being found. 
But pedigree cultures were continued until, on the one 
hand, we succeeded in placing the plants in optimum sur- 
roundings for the production of climax leaves, and on the 
other began to distinguish between the various biotypes. 

The Biotypes 

As has been noted previously, it was possible to use two 
criteria for the classification of the rosets. Leaving out 
of consideration the rosets of the linear-leaved arach- 
noidea, it was f oimd that after dividing the rosets accord- 
ing to the ''broad" or ''narrow" character of the earlier 
leaves (Big. 3), it was possible to further subdivide each 
group on the basis of the marginal indentation of the 
leaves subsequently formed. 

I. The ^' Broad'' Group. — Here the first four or five 
leaves possess a blade which is approximately twice as 
long as broad. Up to this stage the margin remains 
entire. When the sixth leaf appears one ordinarily can 
begin to distinguish between two types. These are : 

Type 1. — In this, the first of the two broad-leaved 
forms, the margin of the first eight leaves remains entire, 

10 Hub, H., ''The Origin of Species in Nature," American Naturalist, 
45: 646, Nov., 1911. 



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No. 568] X CAPSELLA BURS A-P AST OEIS ARACHNOIDEA 201 

showing at most a very slight crenation (Fig. 4). Usually 
the ninth leaf, though sometimes it is the eighth and some- 
times the tenth, shows a more marked indentation, though 
seldom of a depth of more than 2 mm. on each side of 
the leaf and slightly below the middle. Subsequent 
leaves show an increase in the number and depth of the 



Fig. 4. Dissection op Young Rosets of C. . . . simpler and C. . . . rhoin- 

boidea. Showing the " Broad " Character op the Earlier Leaves 

AND the Distinctive Character op the First Sinus. 

indentations, the maximum for both being reached in the 
climax leaves, which usually show five indentations reach- 
ing about midway from margin to midrib. In those of 
the earlier leaves which show a marked incision the lobes 
are obtuse. In the later leaves the lobes become acute. 
It may be stated as a general truth, that an increase in 
the depth of the sinus carries with it an increase in sharp- 
ness of the lobe. There is no secondary lobing, but some- 
times the margin of the sinus shows a slight denticulation. 
While in the earlier leaves the sinuses separating the 
terminal lobe from the rest of the blade are the deepest, 



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202 THE AMERICAN NATURALIST [Vol. XLVHI 

the converse is true in the later leaves, where the sinuses 
separating the terminal lobe are the most shallow. I 
have identified this form with Shull's simplex}^ My 
plants also agree fairly well with the illustration of onto- 
genetic succession of leaf forms in Bursa . . . simplex, 
shown by ShuU.^^ 

Type 2. — In the second of the two forms distinguished 
because of the greater relative width of their first leaves, 
the margin of the first five leaves remains entire, as in 
the case of those of type 1 {simplex). The sixth leaf, 
however, ordinarily shows a marked indentation, at least 
3 mm. deep and slightly below the middle of the blade 
(Fig. 4). This indentation may appear in one margin or 
in both. The lower margin of the sinus ordinarily is at 
right angles to the midrib, the upper margin making an 
angle of 45 degrees with the midrib ( Fig.7, h ) . Even when 
it has become difficult to distinguish between types on the 
basis of relative width of the earlier roset leaves, it always 
is possible to distinguish between tjT)e 2 (rhotnboidea) 
and type 4 {Setchelliana and Treleaseana)^ by means of 
the character of the sinus. In type 4, the lower margin 
of the sinus makes an angle of 45 degrees with the midrib, 
while the upper margin makes an angle of between 30 
and 45 degrees with the midrib. Hence the first sinus in 
C. . . . Setchelliana and C . . . Treleaseana is at least 
90 degrees, while the first sinus in rhomboidea measures 
seldom more than 45 degrees and frequently less. 

The seventh leaf of plants belonging to type 2 ordi- 
narily shows two indentations on both sides of the leaf, 
dividing the blade into a lower portion, two central lobes 
and a terminal lobe. The depth of the incision amounts 
to about three-fourths of the width of the blade from mid- 
rib to margin. 

It is possible to delay the appearance of the first inden- 
tations by transplanting from seedpan to flat either too 
early or too late. In such cases, the indentations appear 
in the seventh leaf only, or even later, and are rather 

11 Loc. city 25, and PI. 2, Fig. 2. 

"Shun, G. H., **Verh. d. naturf. Ver. in Bninn,'' 49, PI. 4, 191L 



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No. 568] X CAPSELLA BURSA-P AST ORIS ARACHNOIDEA 203 

shallow, reaching a depth of three-fourths of the width of 
the leaf from margin to midrib in the eighth, ninth or 
tenth leaf. However, once the indentations have made 
their appearance, the leaf next produced ordinarily shows 
two sinuses on both sides of the blade, usually the upper 
set, rarely the lower, being the deeper of the two, and 
almost reaching the midrib. The succeeding leaves show 
an increase in the number of lateral lobes from two to 
six. Since the incisions almost, if not quite, reach the 
midrib, both lateral lobes and the terminal lobes are well 
defined. Upon the lateral lobes secondary lobes appear, 
both on the distal and proximal margins. It is to be 
noted that only the climax leaves of well-grown specimens 
of the homozygotic form distinctly show the lobing of the 
proximal margin and this only on the middle lobes. The 
lobing of the primary lobes results in the setting off of 
a small terminal portion of each lateral lobe, which 
possesses a more or less rhomboidal form. This terminal 
lobe of the primary lobe can be observed to advantage 
only in the climax leaves of well-developed specimens. 

I have no hesitation in identifying type 2 with ShuU's 
rhomboidea.^^ 

Capsella Bursa-pastoris simplex and C. Bursa-pastoris 
rhomhoidea, described, respectively, as types 1 and 2, 
agree in having the first five or six leaves twice as long as 
broad, thus contrasting sharply with the plants to be de- 
scribed under types 3 and 4, which constitute the *' nar- 
row" group. 

II. The ''Narrow'' Group. — In the plants belonging 
here, the first five or six leaves possess a blade which is 
from 2^ to 3 times as long as broad. Usually after the 
appearance of the seventh leaf, sometimes not until the 
appearance of the tenth leaf, it is possible, on the basis of 
marginal indentation, to separate the plants with ** nar- 
row'' roset-leaves into two groups, designated respec- 
tively types 3 and 4. 

Type 3. — Rosets of plants belonging to type 3 can not 
be distinguished from those of iype 4, until after the 

"ShuU, Verb., PL 2j Biotypes, PI. 1, Fig. 2. 



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204 THE AMERICAN NATURALIST [Vol. XLVHI 

seventh leaf has appeared (Fig. 5). It is to be noted that 
for the first six leaves of type 4, the ratio between mean 
length and width is 6:2, while for the corresponding 
leaves of type 3, the same ratio is 5 :2. Once the seventh 




Fig. 5. Dissection op Young Rosets of x C. . , . Setchelli and x C. . . . 

attenuata^ Showing the " Nabrow " Character op the Earlier 

Leaves and the Distinctive Character op the First Sinus. 

leaf has appeared, a distinction readily can be made, since 
in type 3, no sinuses appear, and the leaves, from the 
seventh to the tenth, might be mistaken for those of 
simplex (Fig. 5). Later leaves readily can be distin- 
guished from those of simplex, by the pointed apex, the 
very shallow sinuses, ending in a sharp tooth, and by the 
fact that the greatest width of the blade lies above the 
middle, about one third the length from the tip (Fig. 6). 

This form, which because of its morphological charac- 
ters on the one hand, and its behavior in breeding on the 
other, can readily be distinguished from all others, I 
designate X Capsella Bursa-pastoris attenuata. 

Type 4. — Not only do the first leaves of plants, belong- 
ing to this type, differ in relative width from the first 
leaves of plants of rhomboidea and simplex, but there also 



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No. 568] X CAPSELLA BURSA-P AST ORIS ARACHNOIDEA 205 

is a difference in the apex of the leaf, the apices of leaves 
of this type, like those of type 3, being decidedly pointed, 
while those of types 1 and 2 are rounded.^* 

At the sixth or seventh 
leaf stage, the marginal 
indentations make their 
appearance, at first as 
slight crenations, then as 
long and shallow sinuses, 
and finally, in the eighth 
or ninth leaf, as a sinus 
on one or both sides of 
the midrib and about the 
middle of the blade (Fig. 
5 ) . The lower margin of 
the first sinus ordinarily 
makes an angle of 45 
degrees with the midrib, 
while the upper margin 
makes an angle of from 
30 to 45 degrees with the 
midrib. This renders the 
first sinus ordinarily 
greater than 90 degrees 
(Fig. 7, a). The depth 
of the first sinus is ap- 
proximately one half the 
distance from margin to 

midrib. In subsequent leaves the depth increases, so that 
in the 11th leaf the sinuses almost reach the midrib. In 
Treleasi, one of the two forms, which together constitute 
type 4, the climax leaves show incisions to the midrib, and 
a well-marked terminal lobe, while in the other the sinuses 
are less deep but the terminal lobe still is well marked 
(Fig. 8). The number of sinuses increases in propor- 

^* It is to be noted that in mj cultures there appear, from time to time, 
plants of rhomhoidea of which the leaves have sharply pointed lobes. What 
relation these plants bear to others classed with them under rhomhoidea, I 
am at present unable to say. 



Fig. 6. Lateb Roset Leaves op w C, 
, . attenuata and C. . . . simplex. 



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206 



THE AMERICAN NATURALIST [Vol. XLVIII 



tion to their depth. If the seventh leaf has one sinus 
in each margin, the eighth and ninth usually have two, 
the tenth and eleventh, three, and so on, until the mean 
of six is reached. As the lobes increase in number, they 





Fio. 7. Early Roset Leaves of x 
C. . . . Svtchein AND C. . . . rhom- 
hoidea. 



Fig. 8. Climax Leaves of x C. 
. . SetchelH and x C. . . . Treleasi. 



not only become narrower but the sinuses do likewise. 
This is the result of a gradual increase in the angle 
between the lower margin of the sinus and the midrib. 
In the eighth leaf the lower margin forms an angle of 
about 90 degrees with the midrib, causing the formation 
of a primary lobe, triangular in shape and with an upper 
angle of about 45 degrees, instead of the 90-degree angle 
found in the first lobe. In older leaves the angle between 
lower margin of sinus and midrib may increase to 110 or 
even 120 degrees. The climax leaves therefore get to 
resemble more and more those of rhomboidea, especially 
since the distal margin of the sinus, from the tenth leaf 
on, exhibits a number of denticulations which, in older 
leaves, especially of one of the forms {Treleaseana)^ 
tend to become incisions, so that secondary lobes are 



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No. 568] X CAPSELLA BVRSA-P AST ORIS ARACHNOIDEA 207 

formed. However, the end of the lobes of early 
leaves of type 4 always are sharply pointed (Fig. 9), 
while the lobes of early leaves of rhomboidea are ordi- 
narily rounded at the ends (Fig. 4). 



Fig. 9. Upper Row : 3 Sets op Leav-es from as Many Plants of jr C. . . . 

TreleasL Lower Row : 4 Sets of Leaves from as Many 

PukNTS OF X C. . . . Setchclli. 

From a morphological point of view these leaves are 
entirely different from any form described by ShuU, the 
differences being most marked and very readily recog- 
nized once our attention has been called to them. But it 
is especially the behavior of the plants on breeding which 
leads me to recognize them as most distinct hybrid forms 
and which I have designated X Capsella Bursa-pastoris 
Setchelliana in honor of Professor William Albert 
Setchell, and X Capsella Bursa-pastoris Treleaseana, in 
honor of Professor William Trelease. 

Type 5. — Capsella Bursa-pastoris arachnoidea. This 
form, which readily is recognized from the first by its 
linear leaves, does not require an elaborate description 
at present, since it will be discussed in detail later. It has 
been illustrated in Figs. 1, 2 and 3. 



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208 



THE AMERICAN NATURALIST [Vol. XLVHI 



The above descriptions apply only to plants grown 
under fairly uniform conditions, in a light soil in a green- 
house, and treated in such a manner as to oflfer the plant 
the most favorable conditions for development. By leav- 
ing the plants too long in the flats, so that crowding re- 
sults, by keeping them too moist and warm, etc., it is 
possible to produce abnormal climax leaves in which the 
typical diflferences can be recognized with difficulty only. 
By leaving plants too long in the seedpans, by keeping 
them too dry, it may be brought about that plants flower 
without having produced climax leaves. There will be 
doubtless many who, because of this, will refuse recogni- 
tion to the segregates just described. **Qu8ecunque dixi, 
si placuerint, dictavit auditor." Fortunately, the differ- 
ences of behavior on breeding are such, we must recognize 
their distinct genotypic constitution. 

Genotypic Constitutions 
ShuU, in the papers above quoted, made one of the most 
important of recent contributions to science, since he de- 
termined with exactitude the relations existing between 
some of the lesser forms which, because of their alleged 
constancy or inconstancy, have been a bone of contention 
since the days of Jacquin. Making extensive cultures of 
Capsella, Shull was able to distinguish four forms (Fig. 
10), to wit, heteris, with leaves divided to the midrib, with 




Fig. 10. 



CL13IAX Leaves of C. . . . 
AND C. 



heteris, C. . 
. . . simplex. 




tenuis 



rhomboidca 



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No. 5d8] X CAPSELLA BURSA-PASTORIS ARACUNOIDEA 209 

elongated primary lobes, a marked secondary lobe, in the 
distal axil of the primary lobe and a well-marked terminal 
lobe ; rhomboidea, with leaves divided to the midrib, with 
an imelongated primary lobe, with an incision in the distal 
margin setting oflf a secondary lobe and a corresponding 
incision on the proximal margin of the primary lobe, set- 
ting off, in well-grown specimens, a terminal portion of 
each lateral lobe, generally of rhomboidal form; tenuis, 
with the elongated primary lobe of heteris, but with a 
sinus which usually does not reach the midrib, terminal 
lobe clear cut; simplex, with lateral lobes obtuse, never 
attenuated, the incisions being shallow and never reach- 
ing the midrib. 

Shull recognized here the presence and absence of two 
factors, one (A) responsible for the sharp primary lobe 
of heteris and the attenuation of the lobes in tenuis, while 
the other (B) is responsible for the division of the leaf 
to the midrib, the definite terminal lobe and the second- 
ary lobes. On this basis Shull was able to represent the 
biotypes by conventional Mendelian symbols, thus: 
heteris, AB; rhomhoidea, aB; tenuis. Ah; simplex, ah. 

That this conventional presentation gives us a reliable 
working basis, my experiments have shown most satis- 
factorily. With the aid of these symbols I have been able 
to solve the origin of Capsella arachnoidea, the experi- 
ments showing that, without question, forms presenting 
the spider-like appearance of the rosets typical of this 
plant are of hybrid origin. 

The Zygotic Constitution of 4,108.6 
The problem to be solved was that of the zygotic con- 
stitution of the original parent, the plant which in my 
notes is recorded as 4,108.6. Among its offspring neither 
heteris nor tenuis made their appearance, while both 
rhomhoidea (aB) ajid simplex (ah) were met with. Hence 
the parent was homozygotic for (a), but heterozygotic 
for (B). Therefore, its zygotic constitution, in part, must 
have been aaBh. 

Besides rhomhoidea and simplex there appeared two 



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210 



THE AMERICAN NATURALIST [Vol. XLVHI 



forms, referred to as types 3 and 4, the latter being ca- 
pable of further subdivision. Neither of these was de- 
scribed by Shull. At least one difference between rhom- 
boidea and simplex, on the one hand, and types 3 and 4, on 
the other, could be noted at once, i. e., the relative width 
of the leaf. As has been shown above, the former have 
their first leaves twice as long as broad, the latter three 
times as long as broad. The idea suggested itself that 
there might exist a factor which determined these charac- 
ters. Since the original parent belonged to type 4, the 
narrow character of the earlier leaves must be dominant 
over the broad character. Also, since the original parent 
produced both ** narrow ^^ and ** broad '^ types, it must 
have been heterozygotic for this character. Using (N) 
to indicate the gene, we get for the zygotic construction 
of the parent plant oaBbNn. 



aBN aBn 



abN 



abn 



aBN 



aBn 



abN 



abn 



1 
aBN 
aBN 


2 
aBn 
aBN 


3 
abN 
aBN 


4 
abn 
aBN 


5 

j aBN 
aBn 

9 

aBN 
, abN 

1 

1 


6 

aBn 
aBn 


7 
abN 
aBn 


abn 

aBn 1 


10 
aBn 
abN 


11 
abN 
abN 


12 

abn 
abN 


13 

aBN 

abn 


14 

aBn 
abn 


16 

abN 
<d>n 


16 1 
abn 

abn 1 



Pig. 11. 



Diagram to Illustrate the Nature op the Offspring or m C. . 
Setchelli (aaBhNn). 



Since self-fertilization is the rule in Capsella, it was an 
easy matter to test the validity of the theory. A form 
aaBbNn, one with unelongated primary lobes, sinuses 
reaching the midrib and with early leaves of a *^ narrow *' 
type should yield, on self-fertilization, the following com- 
binations: l.bbnn (square 16), a plant of which, accord- 
ing to our definition, the earlier roset leaves should be 



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No. 568] X CAPSELLA BUB8A-P AST ORIS ARACHNOIDEA 211 

broad and of which the later leaves shall lack incisions 
reaching to the midrib, a plant, in short, which should 
have all the characteristics of Shull's simplex. Further- 
more, on being self ed, it should yield a uniform offspring, 
in all respects resembling the parent. 

Such plants actually were encountered. Of the plants 
grown to maturity, twelve were selected as seed-bearers. 
All bore the simplex character. Ten of these plants were 
selected from among the first generation of plants of the 
supposed zygotic constitution BbNn, while one parent 
(yielding No. 25,712) was derived from a plant bearing 
the simplex character and another (yielding No. 31,112) 
was derived from a plant which was shown to have the 
zygotic constitution bbNn. 

TABLE I 
EviBENcx or HoMOZTOOTic Characizb of Simplex (hhnn) 



Index 
Nomber 


Number of 
Plants 






Charmoter of 




Index Number of Parent 


Parent 


Grand- 
parent 


25.712 


78 


G»» 


S,n2BRl2P9 


bbnn 


bbnn 


26.912 


22 





S,212BRSPI 


bbnn 


BbNn 


26.312 


42 





S,212CR5PI 


bbnn 


BbNn 


26.612 


187 





S,212FRSPS 


bbnn 


BbNn 


26.712 


180 





S,212HR7P7 


bbnn 


BbNn 


30.012 


276 





8,212C/25P1 


bbnn 


BbNn 


30.112 


108 





8,212^i22P6 


bbnn 


BbNn 


30.212 


60 





8,212Gi26P8 


bbnn 


BbNn 


30.312 


162 





8.2120/26P8 


bbnn 


BbNn 


30.712 


27 





S,212HRSP6 


bbnn 


BbNn 


31.112 


50 





26.012A/27P6 


bbnn 


bbNn 


3.113 


207 





26M2BRIPS 


bbnn 


BbNn 




1.399 











This table offers an excellent illustration of the small 
danger of an accidental cross, even if the plants are not 
guarded, always, of course, when the proper precautions, 
indicated above, are taken. Numbers 26,312 and 30,012, 
as well as numbers 30,212 and 30,312, respectively, offer 
instances of uniform inheritance in plants possessing 
recessive characters only and of which the parents in the 
one case were left tmguarded, in the other caged. Had 

19 In tliis colmnn "G" indicates that the parent plant was guarded, 
"O" that the plant was open-fertilized. In other tables the same abbre- 
viation will be used. 



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21 2 THE AMERICAN NATUBAUST [Vol. XLVIH 

crossing taken place in the case of the nnguarded flowers, 
this wonld^ because of the purely recessive characters 
possessed by simplex, have become apparent at once. In 
all cases the parents were checked by means of herbarium 
specimens or photographs, or both. 

2. hhNN (square 11). According to our hypothesis, a 
plant of this zygotic construction should have the earlier 
roset leaves narrow and the climax leaves should lack 
incisions to the midrib. It also should breed true. A 
plant fulfilling these conditions has not been encountered, 
or rather, its recognition was delayed until the offspring 
of the corresponding heterozygote hhNn could be observed. 
As will be shown, the zygotic combination bbNN yields 
a plant with the external characteristics of arachnoidea. 

3. bbNn (squares 12 and 15). A plant of this zygotic 
constitution should have narrow early leaves and the 
climax leaves should lack incisions to the midrib. On 
self-fertilization it should yield 25 per cent. bbNN, 50 
per cent. bbNn and 25 per cent. bbnn. 



bN 1 bn 
bN 1 bN 


bN bn 
bn bn 



Several plants were foimd which fulfilled the require- 
ments as to leaf characters. Such plants, on being selfed, 
yielded approximately 25 per cent, simplex, which we 
know to have the zygotic constitution bbnn, while about 
50 per cent, bore the parental characters, supposedly rep- 
resented by bbNn. The remaining 25 per cent, clearly 
belonged to the type arachnoidea. In all, 12 plants were 
selected as seed-bearers, some being guarded, others re- 
maining uncaged. The results are given in Table II. 

The totals closely approximate the Mendelian ratio, 
yielding, respectively, bbNN 24 per cent., bbNn 49 percent, 
and bbnn 27 per cent. Having established the identity 
of bbnn (simplex) and bbNn {attenuata)j we are forced 
to recognize bbNN as the zygotic construction of arach- 
noidea. It would be a comparatively easy matter to test 



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No. 568] X CAPSELLA BURSA-P AST ORIS ARACHNOIDEA 213 

this directly, prorided the form arachnoidea produced 
seed. Though I have grown several hundreds of these 
plants, I have obtained in all but eight seeds, and these as 
the result of hybridization. Hence the test must be made 
indirectly through crossing of forms yielding the desired 
gametic combinations. 

TABLE II 
EviDBNci or Heteroztqotic Chakactie of attenuata (hbNn) 







Number of Plants 




Index Number 
of Parent 


Char, 
of 


O 
or 




Index 


» 


^yN 


bblfh 


bbnn 


Char, 
of 


Num- 












Grand- 


ber 


a 
1 


&l 


a 

1 


^1 


a 

i 


*! 




Parent 





parent 


26,012 


19 


25.50 


56 


51.00 


27 


25.50 


S,212BR5PI 


66Arn 





BbNn 


26,412 


8 


7.50 


14 


15.00 


8 


7.50 


S,212DR10PS 


bbNn 





BbNn 


31,212 


16 


14.75 


27 


29.50 


16 


14.75 


2Q,012AR2PI 


bbNn 





bbNn 


31.312 


22 


15.00 


19 


30.00 


19 


15.00 


26,012AR\P2 


bbNn ' 


bbNn 


31,412 


10 


14.25 


25 


28.50 


22 


14.25 


26.012il«lP3 


bbNn 


bbNn 


31.512 


24 


25.50 


47 


51.00 


31 


25.50 


26,012^«1P4 


bbNn \ 


bbNn 


31.612 


2 


2.50 


4 


5.00 


4 


2.50 


26,012^ie6P6 


bbNn 


bbNn 


31.812 


26 


28.25 


54 


56.50 


33 


28.25 


26,012J5«1P3 


bbNn 


bbNn 


31.912 


11 


16..50 


40 


33.00 


15 


16.50 


26,012B«1P6 


bbNn 


bbNn 


3.213 


61 


64.25 


130 


128.50 


66 


64.25 


26,912D/K2P4 


bbNn 


BbNn 


3.313 


70 


61.50 


117 


123.00 


59 


61.50 


26,912Jg:/?6P6 


bbNn 


BbNn 


3.513 


27 


35.50 


71 


71.00 


34 


35.50 


26,912/?iJ6P4 


bbNn 1 


BbNn 


Total . 


296 


308.50 


604 


617.00 


334 


308.50 




1 





Of the twelve parent plants concerned in the above ex- 
periment, five were selected from among the first genera- 
tion of a plant having the supposed zj^gotic constitution 
BbNn, while seven were the direct offspring of No. 26,012, 
which had been shown to yield the three forms, arach- 
noidea, attenuata and simplex, as indicated in Table II. 

Tlhe simplex, obtained by selfing a plant of bhNn, breeds 
true, as indicated in Table I, No. 31,112, a simplex, yield- 
ing a uniform simplex offspring, consisting of 50 indi- 
viduals. 

4. BBnn (square 6). A plant of this supposed zygotic 
constitution should resemble, in all respects, ShulPs 
rhomb oidea, the earliest roset leaves being broad, and the 
incisions of the climax leaves reaching the midrib. It 
should breed true. Five lots, involving four parents, were 
grown. Again it was shown, in the case of No. 26,812 and 



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214 



THE AMERICAN NATURALIST [Vol. XLVIH 



No. 30,612, that the fact that plants are left unguarded 
does not affect results. The parents, in all cases, were 
selected from among the first generation of plants having 
the supposed zygotic constitution BbNn. The results are 
given in Table III. 

TABLE III 
Evidence or Homoztgotic Character of rhomboidea (BBnn) 



Index Number 


No.ofPUnta 


Index Number of Parent 


Char, of Parent 


Gor 


25.812 


20 


8,212J5iJlP6 


BBnn 





26,812 


80 


SM2BR3P2 


BBnn 





27.012 


6 


SA12ER10P6 


BBnn 


G 


27.112 


210 


SM2ERISP12 


BBnn 


G 


30,612 


96 


SA12BR3P2 


BBnn 1 







In all cases the off- 
spring was uniformily of 
the rhomboidea character. 



Bn 


Bn 


Bn 


bn 
bn 


Bn 


bn 


bn 



5. Bbnn (squares 8 and 
14) . Plants of this zygotic 
constitution should resem- 
ble those of the preceding 
group, but on being self ed 
should yield 25 per cent 
homozygotic rhomboidea 
{BBnn) J 50 per cent, het- 
erozygotic rhomboidea 
{Bbnn) and 25 per cent. 
simplex {bbnn). 

These three forms were 
found to constitute the 
offspring of a single plant, 
8,212ffi?lP3, itself an off- 
spring of a plant of the 
supposed zygotic constitution BbNn. This plant, from 

16 Bursa ... 39. 



Fig. 12. Climax Lbavbs of a Hbtbb- 
ozTOOTic C . . . rhomboidea and of a 
HoMOZYQOTic C. . . . rhomboidea. . . 



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No. 568] X CAPSELLA BUBSA-PASTOBIS ABACHNOIDEA 215 

the first, was classified as a rhomboidea. At the present 
time, a photograph of the young roset confirms this 
classification. But two climax leaves, which, in the 
earlier part of these experiments, were deemed suffi- 
cient, show that the sinuses do not quite reach the midrib 
(Fig. 12). Unfortunately, Shull, in the description of 
his No. 054.28,^® does not mention this point, though he 
does point out that **the later rosette-leaves had some 
of the secondary lobes acutish, but not elongated. *' In 
the older climax leaves, even of a homozygous rhom- 
boidea, I find that the secondary lobes disappear. Shull, 
in the description just referred to, is so specific as to the 
typical rhomboidea character of the heterozygote that I 
have hesitated to classify the heterozygotes and the homo- 
zygotes. But the homozygotic rhomboidea, obtained as 
the extracted recessive of a selfed plant of the supposed 
zygotic constitution BBNn, always has sinuses which 
reach the midrib. In other combinations, also, one can 
distinguish between BB and Bb by the relative depth of 
the sinus. For the present, then, we will rely upon this 
character. In the case under discussion (26,612, the off- 
spring of 8,212ffi?lP3, guarded) there were among the 
39 plants 6 which clearly were simplex, the heterozygotic 
rhomboidea was represented by 22 individuals, and the 
homozygotic rhomboidea by 11 individuals, the calculated 
ratio being 9.75 : 19.50 : 9.75. The percentage of simplex 
is far too low, 15.4 per cent., instead of 25 per cent., but, 
considering the small number of individuals concerned, 
the total outcome is fairly satisfactory. It is almost tin- 
necessary to add that in this, as in other cases, the off- 
spring of the various plants is being tested as fast as 
time and facilities permit. 

Type 4. — ^Having shown the presumable correctness of 
our supposition as to the zygotic constitution of the initial 
plant {BbNn)y as far as the presence, appearance and be- 
havior on breeding of simplex, rhomboidea and attenuata 
are concerned, there remains to identify the major group of 
combinations which, in a simple di-polyhybrid, constitutes 



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216 THE AMEBIC AN NATURALIST [Vol. XLVIH 

nine sixteenths of the total offspring and may be uniform 
in appearance, the constitnents being separable only by 
breeding, '*eine heillose Arbeit,'' as Baur has it. For- 
tunately, in this case, it is possible to distinguish readily 
between the various combinations. 

One of the combinations, BBNN (square 1), should 
breed true, being homozygotic for both characters con- 
cerned. We would expect such a plant to have narrow 
first leaves and climax leaves with incisions to the mid- 
rib. Thus far I have not encountered such a plant, some- 
thing which at one time led me to consider the possibility 
of gametic repulsion, in this instance the gamete BN 
being incapable of existence. This supposition seemed 
the more plausible since the two genes B and N well might 
be supposed to be antagonistic, the one being responsible 
for an incision of the leaf to the midrib, the other tending 
to make the leaf, especially the earlier leaves, narrow. 
Were this assumption correct, none of the zygotic combi- 
nations found in squares 1, 2 and 5, 3 and 9, and 4 and 13, 
would be formed, though we would expect the same com- 
bination as occurs in squares 4 and 13 to make its appear- 
ance as the result of the fusion of the gametes bN and 
Bn (squares 7 and 10). 

Were this supposition correct, we should have a case 
similar to that of the sweet pea ** Purple Invincible," and 
we could not expect the gamete (bn) to be formed. Since, 
however, simplex (bbnn) appears in our cultures, this 
theory must be rejected. Eecently also, in culture No. 
30,412, an instance was found in which the guarded parent, 
supposedly of type 4, yielded, not simplex, rhomhoidea, 
attenuata, arachnoidea as well as the parental type, but 
only arachnoidea, rhomboidea and the parental type, and 
in proportions closely approximating a ratio 1:1:2. 

A plant which yielded 25 per cent, rhomboidea and no 
simplex, must have been homozygotic for B, and since it 
yielded also 50 per cent, of type 4, must have been hetero- 
zygotic for N, its zygotic constitution therefore being 
BBNn. Such a plant, on self-fertilization, should yield 
25 per cent, rhomboidea. Provided the homozygote and 



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No. 568] X CAPSELLA BUBSA--PAST0R1S ARACHNOIDEA 217 

the lieterozygote have the same appearance, the remaining 
75 per cent, should resemble the parent (Fig. 9, &). 



BN 
BN 


Bn 
BN 


BN 
Bn 


Bn 
Bn 



But in one case (30,412), the parent being 8,4125i?9P9, 
and open fertilized, the offspring consisted of 26.3 per 
cent, rhomboidea, 46.2 per cent, of the parental type and 
27.5 per cent, arachnoidea. If our supposition as to the 
zygotic constitution of the parent is correct, then the 
zygotic constitution of the arachnoidea in this offspring 
must be BBNN. In the case of a selfed attenuata, we 
found that approximately 25 per cent, of the offspring 
was composed of arachnoidea of the probable zygotic con- 
stitution bbNN. Is it possible that any Capsella, homo- 
zygotic for N, would have the appearance of arachnoidea? 
This seems more than probable, and other evidence, to be 
adduced later, appears to support this view. The history 
of the BBNn is as follows : 

During 1912 I grew No. 8,412 from seeds of a plant 
which resembled the grandparent 4,108.6. It was com- 
posed of 1,079 individuals, among which various types, 
such as '* broad, ^' ** narrow*' and ** linear,'' could be rec- 
ognized. Not all plants were thus classified, a fourth 
group of '* intermediates" being formed, indicating that 
some of the plants, while in certain respects resembling 
simplex and especially rhomboidea (deep lobing, second- 
ary lobes), in other characters more closely approximated 
the '* narrows," since their early leaves had been noted 
as *' narrow." In the light of recent experience, it is easy 
to see why the distinction was made, though at the time 
the conception of the differences was most hazy. Several 
of these ** intermediates" were grown, and of these a 
single one yielded the seed for the next generation. This 
plant had been permitted to flower unguarded, but after a 
number of capsules had developed on the main stalk, this 
was decapitated and the sideshoots were allowed to de- 



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218 



THE AMERICAN NATURALIST [Vol. XLVIII 



velop. At this time the entire plant was caged. Subse- 
quently the seeds of the open fertilized and of the guarded 
flowers were sown separately, with the following results : 



S0,412. Open Fertilized 



Per Cent. 



Planto 



Found I Expected 



30,512. Guarded 
Plants 



Per Cent. 



Found I Expected 



Aracknoidea. . 
"Narrow"... 
Rhomboxdea. . 



27.5 
46.2 
26.3 



40 
67 
38 



36.25 
72.50 
36.25 



21.15 
36.15 
42.70 



52 

89 

105 



I 



61.50 
123 
61.50 



The figures are given separately to again call attention 
to the fact that open fertilization is no hindrance to pedi- 
gree work in Capsella. Since the seeds came from the 
same parent, we may add the results, which gives us 
arachnoidea 23.50 per cent., ** narrow" 40 per cent, and 
rhomboidea 36.50 per cent. The fact that the percentage 
for ** narrow *' is too low and that for rhomboidea too 
high, while the percentage for arachnoidea is within the 
limits of probable error, is probably due to errors in 
classification, since greater weight was laid upon lobing 
of the adult leaves than upon comparative width of the 
earlier ones. The value of this culture lay chiefly in its 
suggestion of a zygotic combination BBNn, which prior 
to that time, on account of the gametic repulsion theory, 
was not supposed to exist. In consequence, a number of 
cultures were made, with the following result : 



TABLE IV 
Evidence of Heterozygotic Char.\cter of Treleaseana (BBNn) 



Index 
No. 



3,813 
3,913 
4,013 
4,213 
4.313 
4,413 



Total 



Number of PlanU 


1 
1 


BBXN 


BBNn 


BBnn 


a 

1 




'd 

a 

1 


4 


Found 


Ex- 
pected 


38 


30 


56 


60 


26 


30 


36 


44.76 


87 


89.50 


56 


44.75 


14 


15.26 


28 


30.50 


19 


15.25 


15 


28.60 


65 


57 


34 


28.60 


33 


33 


62 


66 


37 


33 


37 


45.25 


102 


90.50 


42 


45.26 


173 


196.75 


400 


393.50 


214 


196.75 



Index No. of 
Parent 



30,412^«2P6 
30,412^/?4P3 
30,412^/26P3 
S0A12BR2P6 
30M2BR6P5 
30,412J5/29P2 



Char. 

of 
Parent 



_L 



BBNn 
BBNn 
BBNn 
BBNn 
BBNn 
BBNn 



Char. 

of 
Grand- 
parent 



O BBNn 



BBNn 
BBNn 
BBNn 
BBNn 
BBNn 



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No. 568] X CAPSELLA BURSA-P AST ORIS ARACHNOIDEA 219 

The *' narrows*' in question, then, fulfilled our expecta- 
tion on the basis of a zygotic constitution BBNn. In 
some cases the percentages are too high, in others too low. 
The total yields fairly satisfactory results, to wit: BBNN 
22 per cent., BBNn 51 per cent, and BBnn 27 per cent. 
Two tests of the extracted recessive, a homozygotic rhom- 
boidea, were made. The cultures. No. 3,713, from a 
guarded rhomhoidea (30,412u4B2P3) and No. 4,113, from 
an unguarded rhomhoidea (30,412u4iJ8P3), both derived 
from plants of the supposed zygotic constitution BBNn, 
yielded, respectively, 54 and 207 plants, all of which bore 
the typical rhomhoidea characters. 

In the cultures just tabulated, the plants of the sup- 
posed zygotic constitution BBNn resembled the parent in 
all respects. The form arachnoidea, in this case, must 
have the zygotic formula BBNN. Unfortunately, in this 
case also, it proved imf ertile. 

A better acquaintance with plants of the zygotic consti- 
tution BBNn led us to formulate certain differences be- 
tween them and our original *' narrow.** Plants of the 
BBNn character, readily can be segregated from those of 
the BhNn character by somewhat narrower primary 
lobes, split to the midrib and the development, in climax 
leaves of well-grown specimens, of a secondary lobe, not 
pronounced but recognizable (Figs. 8, 9). 

On the basis of these morphological differences, as well 
as because of the behavior of the plant on breeding, I 
propose to segregate it from type 4 under the name 
X Capsella Bursa-pastoris Treleaseana. This form is 
homozygotic for B, while Setchelliana is heterozygotic 
for B. Both are heterozygotic for N. They may be ex- 
pected to look alike during the early stages. Later they 
show a difference, since the form containing Bh does not 
develop sinuses as deep as the form containing BB. The 
form Treleaseana, when young, can readily be distin- 
guished from a heterozygotic rhomhoidea (Bbnn) by the 
relative width of the early leaves ; later such a distinction 
is diflScult (Figs. 4, 5, 7). If any distinction at all is to 
be made, it should be made on the basis of the rounding 



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220 THE AMERICAN NATUBAZI8T [Vol. XLVUI 

of the lobes, those of Treleaseana being sharp, those of 
the heterozygotic rhomboidea rounded. 

I am fully aware that in thus naming genotypes, I am 
departing from all rules laid down by systematists. But 
a rule is useful only as long as it serves a purposed For 
the geneticist, the rules of systematists are of small value. 
Subspecies, variety, form, are, after all, but very general 
terms, almost incapable of definition because of too fre- 
quent abuse. But once we have determined the zygotic con- 
stitution of any plant, we have placed ourselves on a firmer 
basis. Behavior in breeding is the proper criterion. And 
while I recognize that this, for systematic purposes, is 
impracticable, at the same time I assert the right to use 
a trinomial for any organism of known zygotic constitu- 
tion, this being, at the present time at least, the easiest 
way of designating any particular form. Some day we 
shall have formulas, corresponding to those of chemistry, 
to designate the lesser forms. 

The increase in the number of named forms, a neces- 
sary consequence, need cause no alarm, since they concern 
only him who occupies himself with one species exclu- 
sively. But we must go even further than this. Squarely 
facing the issue, we find ourselves placed in apposition 
which necessitates the naming of heterozygotes. Obvi- 
ously, numerous objections could be urged. But since it 
has been shown, on the one hand, that certain forms can 
exist only in a heterozygous form (Baur^s Antirrhinum) 
and, on the other, that not only the difference between the 
homozygote and the heterozygote is as great as that be- 
tween many of our ** systematic '^ species (for instance, 
attenuata, bbNn, and arachnoidea, bbNN)j but that a 
homozygotic condition for a single gene gives the same 
result, whatever the condition of the other known genes, 
at least as thus far determined (arachnoidea occurs as 
aaBBNN, aaBbNN and aabbNN)^ the advantage of nam- 
ing all forms of different zygotic constitution must be 
granted. 

Thus far we have not encountered a plant of the zygotic 
c<mstitution BbNN, at least as far as can be judged from 



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Na 568] X CAPSELLA BURSA-PASTOBIS ARACHNOIDEA 221 

breeding experiments. On being selfed such a plant 
should yield : 



BN 
BN 


bN 
BN 


BN 
bN 


hN 
bN 



It has been shown that plants of the zygotic constitu- 
tion BBNN and bbNN exhibit the arachnoidea type. At 
least 50 per cent, of the offspring then should show this 
character. But if the suggestion made above is the cor- 
rect one, i. 6., that all plants homozygotic for N exhibit 
the arachnoidea type, then the parent and its entire off- 
spring should bear this character. The unfortunate in- 
fertility of arachnoidea prevents us from submitting this 
hypothesis to direct experimental proof. But there exist 
indirect means for establishing the probable truth of our 
contention. In the first place, we may cross two plants, 
the identity of which can be established beyond doubt, to 
wit, attenuata (bbNn) and Treleaseana (BBNn). Such a 
cross would yield : 



BN 

bN 


Bn 
bN 


BN 

bn 


Bn 
bn 



Of these, we would recognize Bbnn because of its rhom- 
boidea character, 50 per cent, would be recognized as 
Setchelliana (BbNn), while the remainder, if our surmise 
is correct, would consist of arachnoidea. Experiments to 
determine this are under way. At the present we have 
another, though by far less accurate, means of testing our 
hypothesis. If the combination NN always results in a 
form arachnoidea, the offspring of a plant of the zygotic 
constitution BbNn would be composed of : 

4 Setchelliana (BbNn), 

2 Treleaseana (BBNn), 

2 attenuata {bbNn), 

4 arachnoidea (1 BBNN, 2 BbNN, 1 bbNN), 



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222 



THE AMEBIC AN NATURALIST [Vol. XLVHI 



3 rhomhoidea (1 BBnn, 2 Bbnn), 

1 simplex (bbnn). 
Since BbNn, BBNn and bbNn, in the earlier experi- 
ments, might have been confonnded in the later stages, 
and since there is little doubt as to the earlier stages, 
these three forms have been combined in Table V. 



TABLE V 
Besults from Selected Setchetliana (BbNn) 



Index 


"Narrow" 




rhomboidea 


simplex 


No. 


Foand 


Expected 


Found 


Expected 


Found 


Expected 


Found 


Expected 


26.912 
3,613 


134 
94 


167.6 
89 


94 
45 


78.8 
45 


68 
33 


59.1 
33.75 


19 
8 


19.7 
11.25 



This, especially in the case of No. 3,613, is a fairly close 
approximation to what we might expect. When in No. 
3,613 we attempt to distinguish between Setchelliana, 
Treleaseana and attenuata, we get the following num- 
bers, the expected numbers following in parentheses: 
BbNn 39(45), BBNn 21(22.50), bbNn 34(22.50), the last 
number being far too high. When the experiments were 
begun, we distinguished only between '* narrow," 
'* broad'' and ''linear.'' To-day we know that the ''nar- 
rows" include Treleaseana, Setchelliana and attenuata, 
that the "broads" include rhomboidea and simplex, while 
the linears are identical with arachnoidea. In this light 
it is of interest to go back to the first generation of 1910. 
Our data yield the figures given in Table VI. 

TABLE VI 





"Narrow" 


"Linear*' 


"Broad" 


Index No. 
















Found 


Expected 


Found 


Expected 


Found 


Expected 


7,911 


34 


30.50 


9 


15.25 


18 


15.25 


8,111 


27 


35.50 


16 


17.75 


28 


17.75 


8.311 


66 


61 


32 


30.50 


24 


30.50 


8.711 


27 


27 


15 


13.50 


14 


13.50 


8.811 


49 


46.50 


20 


23.25 


24 


23.25 


9,011 


4 


7.50 


4 


3.75 


7 


3.75 


9,511 


93 


76 


32 


38 


27 


38 


9.611 


28 


23.50 


6 


11.75 


14 


11.75 


Total 


328 


308.50 


133 


154.25 


156 


154.26 


Per cent 


53.2 


50 


21.5 


25 


25.3 


25 



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No. 568] X CAPSELLA BURSA-P AST OBIS ABACHNOIDEA 223 

It must be granted that the approximation is fairly 
close, and that, taken in consideration with the others, it 
offers ample support for the correctness of the diagnosis 
of the zygotic constitution of the original plant. It at 
least offers a working basis. One would be tempted to 
accept it as a final solution were it not for the fortunate 
appearance of a plant which does not fit into our scheme 
and which, provisionally, has been nsuxiedCapsella Bursa- 
past oris orbicularis. 

Capsella Bubsa-pastobis obbiculabis 
This form differs from any other plant encountered 
in my cultures. While in a general manner resembling 
simplex, it differs in being more robust, having larger 
flowers (though not as large as those of C. grandiflora)^ 
and in having orbicular first 
leaves (Fig. 13). All leaves 
are covered with stout hairs. 
It is a plant which tempts us 
to draw a parallel between it 
and (Enothera gigas, a name 
which I have not used for the 
sake of avoiding an impUed .'^;''^^,«^''"''*'' ''^ '^' 
comparison. 

The first plant of this type appeared in a culture of 
attenuata (26,0125B3P5) and was of sufiSciently striking 
appearance, though but four or five leaves had developed, 
to call for a special note and a photograph. Later the 
plant was potted and finally seed was gathered from the 
unguarded plant. From this seed four seedlings were 
obtained. At least three of them closely resembled the 
parent, the fourth having somewhat narrower leaves. 
Later the differences between these plants and those of 
simplex became more apparent (Fig. 14). Those of my 
students to whom the differences have been pointed out 
have not the slightest difficulty in distinguishing between 
the two forms. It is hoped that later, when by means of 
prolonged cultures I shall have made myself more familiar 
with this form, it may be made the subject of a distinct 
paper where histological and cytological studies will find 




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224 THE AMEBIC AN NATURALIST [Vol. XLVm 

a place. One would be inclined to look upon orbicularis 
as a mutation. But the fact that at first we classed 
arachnoidea as such, later to prove it of hybrid origin,^^ 



Fio. 14. Four Seedlings of C . . . orbicularis and (the lower) Two Seed- 
linos OF C. . . . simplex. 

would tend to make us cautious, and lead us to attempt to 
find a solution for the origin of orbicularis in the disso- 
ciation or combination of certain * * units. ' ' While I should 
not care to go quite as far as M. Heribert Nilson'® **das 
ganze Mutations phanomen durfte unter einen gemein- 
samen Gesichtspunkte : der Mendelschen Neukombination 
eingeordnet werden konnen," yet it is probable that here 
the majority of alleged mutations may be classed. 

iTBaur's (Vererbungslehre, 189) narrow-leaved Melandrium album is 
perhaps susceptible of the same explanation. 

i^Zeitschr. f, ind. Ahst. «. Bcrerh., 8: 89, 1912. 



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No. 568] X CAPSELLA BURSA-F AST ORIS ARACHNOIDEA 225 

An examination of the herbarium material placed at 
my disposal reveals the fact that plants, apparently 
identical with C. orbicularis, occur in Europe. In the 
Engelmann herbarium of the Missouri Botanical Garden 
are two sheets (No. 3,661 and 3,664) containing specimens 
which undoubtedly must be classed here. The latter sheet 
bears the label : Thlaspi Bursa-pastoris humUe. Heidel- 
berg. April 1828. 

A culture of Capsella, derived from seed of a single 
plant, unfortimately not preserved, escaped from culti- 
vation in the Experiment Garden, and consisting of 182 
individuals (Ehlers, No. 4,813), appears to be composed 
entirely of orbicularis. And while I have never encoun 
tered the plant in nature, these two facts lead us to another 
possible explanation. Perhaps the appearance of orbic- 
ularis in the original culture was due to an accidental 
admixture, such as is almost impossible to guard against 
when experimental plants are grown in a greenhouse used 
for a variety of purposes. 

The exact relation which orbicularis bears to the other 
types of Capsella here described can, of course, be de- 
termined only after a series of experiments has been car- 
ried out. However, the delay in the completion of the 
manuscript, caused by the unfortunate destruction, by 
fire, of the botanical laboratories of the University of 
Michigan, enables me to add that a third generation of 
orbicularis, the parent being No. 32,012B1P3, shows at 
least two and possibly three types, of which one is espe- 
cially interesting in having rather narrow leaves, at least 
as compared with those of typical orbicularis. The con- 
trast between the two forms is increased by the fact that 
in the narrow-leaved form the foliage is entirely glabrous, 
while in the typical orbicularis the leaves are covered 
with numerous stiff, almost bristle-like, hairs. 

X Capsella Bubsa-pastobis abachnoidea 
By this name is designated the linear-leaved form, the 
appearance of which induced us to undertake the cultiva- 
tion of Capsella Bursa-pastoris Setchelliana. 



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226 THE AMERICAN NATURALIST [Vol. XLVIII 




FKJ. l.'i. I{r)SKT.S iLI.rSTUATING Tl.K Two TYPKS 



Already the leaves which immediately follow the coty- 
ledons serve to distinguish plants of this type from all 
others. At the ten-leaf stage even the casual observer is 
able to segregate them at once from the other rosets. 
The leaves are acicular and the cotyledons far larger 
than those of the seedlings of the other forms. The 
greater size of the cotyledons may be attributed to the 
insufficiency of the subsequent leaves. 

If one removes the terminal bud of seedlings of Atri- 
plex hortensis or one of its color varieties, it will be found 
that the cotyledons increase in length far beyond normal, 
sometimes reaching a length of 8 cm. Under favorable 
conditions the leaves of X C. arachnoidea may rfeach a 
length of 100 mm., with a greatest width of 6 mm. (Fig. 
16). The stem ordinarily is weak, having a diameter of 
only 1 mm. It may reach a length of 30 cm. (Fig. 17). 



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No. 568] X CAPSELLA BURSA-P AST OBIS ABACHNOIDEA 227 



fiijs J^AK Recognized in C. . . . orbiculaHs. 



Th 



^ 



flowers are small, the petals especially so. The 



^^x^s shrivel up early and as a rule are devoid of polleu 

^^^^'^^^^ Occasionally a few can be demonstrated. The 

ovatr^,-^ though small, contains what appear to be ovules 

.^^•^Xe of being fertilized. Thus far I have collected 

f ^ :seeds contained in 6 capsules on unguarded plants 

^ ^^^^^<;hnoidea (Fig. 18). Two of these germinated, the 

^ ^ ^5^ ielding a plant which looks like simplex, though 

ua^xx^^ a large amount of red coloring matter in the peti- 

oVfe^^ "While the other is an arachnoidea. Attempts to arti- 

\ tvc\^lXy fertilize arachnoidea have failed absolutely. 

, ^^ has been shown above, one may distinguish, on the 

"^ V^'^i.H of genotypic constitution, three forms of arach- 

"^^ v^oidea, viz.: BBNN, BbNN and bbNN. Externally no 



^'v^. 



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28 



THE AMERICAN NATURALIST [Vol. XLVffl 



ifferences can be noted. A single exception perhaps may 
e made to this statement. It had been noted that speci- 
lens of arachnoidea frequently showed f asciation. This 
isciation seems most marked in plants of the zygotic 
institution BBNN (Figs. 19, 20, 21). 



Fig. 16. Roset of x C. , 



arachnoidea. 



While it is hoped that later a more extended report r^Sigr /> 
B made upon this plant, at present it may be stated tj^^ 
lere exists the probability, that it may throw some li^i^? 
pon the nature of fasciations. In earlier publication^! » 
have brought together some of the known facts bearing 
pon this teratological character. Though a large por^ 

19 < < Fasciation in Oxdlis crenata and Experimental Production of Fascia. 
ons," Bep, Mo. Bot. Gard., 17: 147, 1906; "Fasciations of Known 
lusation, * ' American Naturalist, 42 : 81, 1908 ; ' ' Inheritance of Fascia- 
on in Zea Mays," The Plant World, 14: 1911; "The Origin of Species 
Nature," American Naturalist, 45: 641, 1911; " Frondescence and 
Etfciation," Plant World, 14: 1911; "Fasciation in Oxalis crenata," 
otanical Journal, 2: 111, 1913. 



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No. 568] X CAPSELLA BURSA-PASTORIS ARACHNOIDEA 229 

tion of the experimental garden is devoted to cultures of 
fasciated races, nothing further has been determined than 
that the fasciated character is inherited, that it is trans- 
mitted through non-fasciated individuals, that its ap- 
parentness depends upon nutrition, that it behaves as a 



Fig. 17. Two Hebbarium Specimens of x C. . . . arachnoidea. 

recessive character and that the fasciated character of the 
stem appears to be associated with split leaves and cup- 
shaped leaves. In a paper read before the Research Club 
of the University of Michigan on March 16, 1910, and an- 
nounced under the title ''The Identity and Inheritance of 
Teratological Characters,^* I showed that split leaves, 
ascidia, certain disturbances in the arrangement of the 



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230 



THE AMERICAN NATUBALIST [Vol. XLVin 



flowers, supemumerary locules in the fruit, etc., may 
safely be taken as an indication of the presence of the 
fasciated character. More recently, Kajanus,2<> working 




Fig. 18. Shoot of x C. , . . arachnoUleu, with a Large Number of Infertile 
AND Few Fertile Capsules. 

with different material, has fully confirmed the views 
which I expressed at the time. This is of particular in- 

20 Kajanus, B., "Polyphyllie und Fasziation bei Trifolium pratense L.," 
Zeiisch, /. ind, Ahst, u, Vererh., 7: 63, 1912; '*Ueber einige vegetative 
Anomalien bei Trifolium pratense L., ibid., 9: 111, 1913. 



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No. 568] X CAPSELLA BURSA-P AST ORIS ARACHNOIDEA 231 

terest in connection with Capsella arachnoidea, since 
many of the plants which do not show a fasciated stem 
do show split leaves (Fig. 20) and a most peculiar whorl- 
ing of the flowers (Fig. 21). 



Fig. 19. Fasciated Plant of a* C . . . arachnoidea. 

The spatulate condition of the leaves of the seedling 
shown in Fig. 2 is believed to have been due to fasciation. 

Capsella Bursa-pastoris arachnoidea, then, bears all the 
earmarks of a fasciated race. All of the three zygotic 
combinations which yield the arachnoidea type are homo- 
zygotic for N. The recent work of East and Hayes, and 
of Emerson on Zea Mays has shown that the fasciated 



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232 



THE AMERICAN NATURALIST [Vol. XLVIH 




Fig. 20. Leaves of x C aruchnoidea. 




Fig. 21. ABNORMAL Whorled Arrangement op the Flowers in Inplokbs- 
CENCES OF w O. , , , arachnoidea. 



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No. 568] X CAP8ELLA BUR8A-P AST OBIS ARACHNOIDEA 238 

character is dominant, though Mendel, in his experiments 
with Pisum umbellatum, has shown it to be recessive. 
No fasciation, thus far at least, has been noted in the 
other forms used in these experiments. 

SUMMABY 

A culture of Capsella Bursa-pastoris proved heterozy- 
gotic, yielding certain new forms (X C. Bursa-pastoris 
SetchelUana, xC. Bursa-pastoris Treleaseana, XC. Bursa- 
pastoris arachnoidea and X C. Bursa-pastoris attenuata)^ 
as well as certain forms already described by ShuU (C 
Bursa-pastoris rhomboidea and C. Bursa-pastoris sim- 
plex) in the proportion 4:2:4:2:3:1. The distinction 
between simplex and rhomboidea, both inter se and be- 
tween them and the other forms, is readily made by any 
one familiar with Shull's investigations. These two 
plants agree in having the earlier leaves broad (Fig. 4). 
The climax leaves of rhomboidea and simplex show 
marked differences, especially as far as the incision of 
the blade is concerned. These incisions, in simplex, reach 
a depth equal to approximately one fourth of the width 
of the blade (Fig. 10). In rhomboidea the incisions are 
deeper, reaching the midrib in the homozygous form 
(Fig. 12). The leaves of the latter also show marked 
secondary lobes. 

The distinction between X C. Bursa-pastoris Setchelli- 
ana, X C. Bursa-pastoris Treleaseana and X C. Bursa- 
pastoris attenuata is made with greater difficulty. They 
agree in having long and narrow first leaves. The climax 
leaves of Treleaseana and SetchelUana show marked 
incisions, exceeding one fourth of the width of the blade, 
and which may reach the midrib (Fig. 9). The latter 
form also may show marked secondary lobes. 

Besides the phenotypes here mentioned occur two 
others, the one, X C. Bursa-pastoris orbicularis, with an 
almost orbicular first leaf (Fig. 13) and a climax leaf 
greatly resembling that of simplex (Figs. 14, 15), though 
differing in texture. This form has not been sufficiently 
studied, but is believed to be identical with one known to 



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234 THE AMERICAN NATURALIST [Vol. XLVIU 

occur in Europe. Finally there is X C. Bursa-pastoris 
arachnoidea, a sterile, linear-leaved form, with a weak 
stem and which frequently shows fasciation (Figs. 17-21). 
To facilitate a distinction between these forms, a key is 
appended : 

a. Early leaves broad. 

h. Early leaves orbicular. orbicularis, 

&6. Early leaves twice as long as broad. 

c. Climax leaves incised to midrib. rhomboidea. 

cc. Early leaves not incised to midrib. simplex, 

aa. Early leaves long and narrow. 

b. Early leaves acicular. airachnoidea, 

bb. Early leaves 2^-3 times as long as broad. 

c. Climax leaves not incised to midrib. atienuaia. 

cc. Climax leaves incised to or almost to the midrib. 

d. Secondary lobes pronounced. Treleaseana. 

dd. Secondary lobes absent. Setchelliana. 

It was found that, besides the genes A, B, C and D, 
whose existence was shown by ShuU, there exists another 
gene, N, responsible for the narrow character of the 
earlier leaves. For the various forms, mentioned here, 
the following zygotic constitutions have been tentatively 
determined: simplex, bbnn; rhomboidea, BBnn and Bbnn; 
Setchelliana, BbNn; Treleaseana, BBNn; attenuata, 
bbNn; arachnoidea, BBNN, BbNN and bbNN. The zygo; 
tic constitution of orbicularis has not been determined. 

As to the probable origin of X C. Bursa-pastoris Setch- 
elliana, little can be said. It most probably results from a 
cross between rhomboidea and attenuata {BBnn X bbNn). 
This seems the most plausible explanation since, judging 
from herbarium specimens, both attenuata and rhom- 
boidea occur throughout the United States. Unfortu- 
nately such an assumption necessitates an explanation of 
the origin of attenuata. 

My thanks are due to the regents of the University of 
Michigan for the facilities placed at my disposal, to head- 
gardener Adolph Weiner for his constant care of the ex- 
perimental plants, to Messrs. J. H. Ehlers, A. Povah, C. 
Oberlin and A. W. Murdock for assistance in classifica- 
tion of the seedlings and to the director of the Missouri 
Botanical Garden for the loan of herbarium material. 



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No. 568] X CAPSELLA BURSA-PASTORIS ARACHNOIDEA 235 

Conclusions 

1. Besides the genes {A, B,C, D) discovered by Shull, 
there exists in Capsella a gene N, responsible for the nar- 
row character of the early leaves of certain forms. 

2. Absence of the gene N results in the formation of 
early leaves of a *' broad'' character. 

3. The form designated arachnoidea is of hybrid origin, 
as are the forms Setchelliana, Treleaseana and attenuata. 

4. X Capsella Bursa-pastoris arachnoidea is formed 
whenever the plant is homozj'gotic for N, whatever the 
constitution of the remainder of the zygote {BBNN, 
BbNN, bbNN), i. e., a homozygous condition for the pres- 
ence of a single factor may overshadow the influence of 
others. 

5. Homozygocity for a single factor may be responsible 
for total, or almost total, sterility. 

6. A knowledge of the early stages, as well as of the 
climax leaves, is essential for the classification of the 
phenotypes of Capsella Bur sa-past oris. 



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BIOLOGY OF THE THYSANOPTERA. H 

DR. A. FRANKLIN SHULL 
University of Michigan 

II. SEX AND THE LIFE CYCLE 

Intkoduction 

From observations made on the abundance of males in 
several species, Jordan (1888) was led to believe that 
there might be among Thysanoptera, as in aphids, an 
alternating life cycle ; that is, that there might be a series 
of parthenogenetic generations during the summer, fol- 
lowed by a generation of males and sexual females in the 
latter part of the summer or in the fall. Coupled with 
this he suspected that there were winged forms in the 
parthenogenetic part of the cycle, and at least occasional 
wingless individuals in the sexual phase. 

Uzel (1895), however, was unable to detect any indica- 
tions of such a cycle. He held that there could be no 
question of parthenogenesis in a species in which males 
were abundant all the time or at intervals. Only in spe- 
cies in which the males were too rare to impregnate all 
the females would he admit parthenogenesis. To prove, 
in such a species, an alternating cycle like that of the 
aphids, it must, in UzePs opinion, be shown that the males 
are abundant only at certain seasons. As Uzel was ac- 
quainted with no European species in which males were 
plentiful at but one season, he rejected Jordan's sugges- 
tion regarding an alternating cycle, and his view seems 
to have been accepted by thysanopterists since that time. 

To Uzers argument it may be objected that the pres- 
ence of males, and even the occurrence of copulation, is 
no proof that parthenogenesis is wanting. For among 
the aphids and rotifers, the parthenogenetic and sexual 
females exist side by side. Nor is parthenogenesis in 
these two groups facultative (optional), as Uzel appears 
to assume for Thysanoptera; a female is either only 

236 



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No. 668] BIOLOGY OF THE THTSANOPTERA 237 

sexual or only parthenogenetic. Moreover, in the roti- 
fers, females incapable of fertilization copulate as fre- 
quently as do those requiring fertilization, as was first 
shown by the work of Maupas (1890) on the rotifer 
Hydatina. 

Presence of males and occurrence of copulation are, 
therefore, no proof of sexual reproduction. But even if 
we accept, as Uzel does, this criterion of sexuality, Jor- 
dan's view that there may be an alternating cycle would 
receive some support if it could be shown that males are 
more abundant at one season of the year than at other 
times. Casual observations made by me several years ago 
seemed to indicate this seasonal variation in the abund- 
ance of males. As the data then available were meager, 
no conclusion was drawn, but I subsequently undertook 
to obtain such data on a larger scale, by making extensive 
collections at all seasons of the year to determine the sex 
ratio. The following pages give these data, along with 
other observations bearing on sex or the life cycle. 

I desire to acknowledge the assistance of my wife, by 
whom much of the labor of determining species and 
counting the sexes was done. 

The Sex Ratio in Vabious Species of Thysanopteba 
In making collections for the purpose of determining 
the sex ratio, the food plants were examined very care- 
fully, torn apart if necessary, and every individual cap- 
tured. This precluded the possibility of obtaining an 
erroneous sex ratio because one sex was more easily dis- 
turbed than the other. A few individuals escaped, but 
they could not have affected the sex ratio very greatly, 
and it was known from their size that they were some- 
times of the one sex, sometimes of the other. 

The sex in the suborder Terebrantia is readily deter- 
mined by the presence of an ovipositor in the female and 
the rounded end of the abdomen in the male. In the sub- 
order Tubulifera, the sex in Anthothrips verhasci was 
determined by the presence of two short, heavy spines, 



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238 THE AMEBIC AN NATURALIST [Vol. XLVm 

one on each side of the abdomen of the male, near the end. 
As the specimens, when placed on a microscope slide, 
nearly always lie either on the dorsal or ventral side, 
these spines are nearly always readily visible if present. 
I used this criterion (mentioned in the re-description of 
the species by Hinds, 1902) only after having taken eleven 
pairs of this species copulating in nature, and observing 
in every case that the male possessed these spines, and 
that in the female they were wanting. In .other Tubu- 
lifera, e. g., Anthothrips niger, sex was determined by the 
longitudinal chitinous rod in the next to the last abdomi- 
nal segment of the female. When the specimens were too 
opaque to observe this rod, they were cleared by boiling 
in caustic potash. 

The data from these collections are given in the accom- 
panying table. Unfortunately the collections could not 
all be made in one year, nor in the same locality. Those 
made from July 1 to September 18, 1912, were made at 
the University of Michigan Biological Station, Douglas 
Lake, Michigan; all others were made at Ann Arbor, 
Michigan. It is not probable that the results are greatly 
modified by collecting in two regions within the state. 
In this table the larvae of all species are combined, as I 
am unable to distinguish with certainty the larvae of 
several of the species here mentioned. 

The important facts contained in this table are, it seems 
to me, the following : 

Euthrips tritici appeared in spring at first only in the 
female sex. Males were first collected nearly a month 
later, and not until about the time fairly large larvae were 
found elsewhere. Once the males appear, though their 
number fluctuates in the individual collections, they fur- 
nish a fairly constant proportion of the whole number 
(about one third). 

The males of Anthothrips verbasci appear in the earli- 
est collection of this species, and in considerable numbers 
throughout the season. The total proportion of males is 
23 per cent., and the only considerable increases over 



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No. 568] 



BIOLOGY OF THE THYSANOPTERA 



239 



this percentage in individual collections are in the three 
collections made in August, and on October 7. Consider- 
ing the large majority of females taken September 12, the 
abundance of males October 7 may be due in some way to 

TABLE I 

Showing Number of Males and Females of the Commoner Species of 
thysanoptera captured at intervals during the active season 



Date 



Apr. 30, 1911 
May 5 

10 

17 

22 

24 
June 



July 



1912 



Aug. 



Sept. 



Oct. 



Nov. 



1 

7 
15 
21 
29 

3, 

4 

5 
11 
16 
17 
19 
26 
27 
29 
30 
31 

5 

8 

9 
12 
13 
18 
20 
21 

2 

2, 
12 
16 
18. 1912 

7, 1911 
14 
25, 1912 

9 



1911 



Enthrips 
tritici 


tkripg 
verbagk'i 


Antho- 
thrips 
niger 


9 cf 


9 cf 9 cT 


9; 




1 


7| 






2| O! 




17l 


1 


22 1 




30 2 


174 


30 20 


41 17 






18 



40 62! 52 10 42 

21 27; 47 8 18 

11 



87| 

11 gI 

14! 25: 



21 

^! 

7 

6 

12 

3 
21 



7 
01 
3! 
2 
1 
29 

0, 




82 



4' 

I 4 

1 

7i 

29 2 



154;i51 

81 1 
16 13 



43 25 



58 15 



30, 20 



26' 18| 



Total . 



16 

3 

7 

15 

3 

13 
4 

19 
3 



18 



88 



23 



1 



17i 

I 

ll 
27 



I I 



879|441 64l'200'l62' 226' 530!l74 50 





Ch 


ro- 




» 


thrips 




us 


jnani- 


Larvae, 




catus 


all 




--_ - - 


Species 


f 


9 


& 




3 












7 






6 


7 


i 


3 


2 


1 


25 


1 






1 


7 


1 





5 
46 
72 




2 





1 




187 


1 


16 
3 




5 


3 
2 








4 


9 






12 




1 


51 


1 









39 


1 











1 






2 103 


2 








1 













2 


36 


21 
13 
10 


2 






2 
18 




1 





4 

4 

12 




2 







4 






2 











36 


203 


191 





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240 THE AMERICAN NATURALIST [Vol, XLVIH 

the dying of their food plants ; but the greater proportion 
of males throughout August is probably significant. It 
should also be stated that I have collected adults of this 
species, of both sexes, from dead mullein spikes in late 
winter. 

Anthothrips niger was found only in the female sex. 
There are no records of males of this species, so far as I 
am aware, in any published work. 

Thrips tabaci was taken almost exclusively in the 
female sex, the two males found September 2 being the 
only ones I have ever collected. 

In Anaphothrips striatus the total number of males is 
less than 25 per cent. On August 20 and September 2 the 
proportion of males is considerably greater than 25 per 
cent., especially on the former date, while at other times 
the proportion was nearly always less. The collection on 
August 20 can hardly have been erroneous by chance, for 
the figures given for that date are combined figures for 
two collections from different localities. In one of these 
collections there were 13 females and 14 males, in the 
other 26 females and 34 males. This strengthens the 
probability that the excess of males is significant. 

Thrips physopus was collected in small numbers, but 
shows a fairly constant proportion of males. 

Chirothrips manicatus presents curious phenomena. 
All the collections up to the end of July were made on 
timothy heads in a small patch a few feet square near the 
laboratory. On July 11 careful search revealed numer- 
ous females, but only one male. By July 19 almost all 
the thrips of this species were gone; only 5 specimens 
were obtained, and these were females. Less than two 
weeks later, however (July 30), on other timothy heads 
in the same small patch, there were foimd 51 males and 
but 1 female. No living thrips were taken here later, as 
the timothy died; but subsequent collections elsewhere, 
from timothy and bluegrass, show again almost ex- 
clusively males. 



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No. 568] BIOLOGY OF THE THYSANOPTERA 241 

Additional Data Beabing on the Life Cycle and Sex 

In view of the fact, to be discussed later, that Anapho- 
thrips striatus has hitherto been known ahnost exclu- 
sively in the female sex, and is known to reproduce par- 
thenogenetically, and the fact that in the collections here 
recorded the males constitute nearly 25 per cent, of the 
total, the question arises, are these males functional f If 
not functional in this species, are the males functional in 
other species! A number of observations and experi- 
ments I have made bear on these questions. 

A single pair of Anaphothrips striatus was found copu- 
lating in nature, which Uzel would have considered proof 
that parthenogenesis did not occur. The testes of the 
males are plainly visible without dissection. Suspecting 
that they might not be fleshy organs at all, but chitinized 
structures, perhaps vestiges of testes, I boiled a number 
of specimens in caustic potash. The testes disappeared, 
from which I judge they are not merely chitinous bodies. 
I can say nothing of their cellular nature, owing to the 
loss of material killed and fixed for that purpose. Nu- 
merous sections of another species Anthothrips verhasci, 
however, reveal well-developed testes. Cell divisions 
(probably the spermatocyte divisions) and nearly mature 
spermatozoa in bundles were observed in these sections. 
Though the number of chromosomes could not be deter- 
mined, it is an interesting fact that spindles in side view 
usually showed a lagging chromosome. 

Finally, with further regard to the functioning of 
males, I have attempted to breed several species par- 
thenogenetically. The results in thfe case of Euthrips 
tritici were so far encouraging that two larvae appeared 
on the plant on which virgin females had been previously 
placed. But in these cases I could not be certain that the 
food plant was uninfected. Experiments with Anapho- 
thrips striatus and Anthothrips verhasci gave negative 
results, but in each case failure to obtain young by par- 
thenogenesis may have been due to the conditions. 

Some observations on the place of pupation may also 



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242 THE AMERICAN NATURALIST [Vol. XLVm 

be here recorded. The rarity with which the pupae of 
most species are discovered in collecting suggested that 
they might not pupate on the food plant of the larvaB. 
Some species of thrips, for example, the pear thrips 
{Euthrips pyri), are known to pupate in the ground 
(Moult on, 1912). Since many of the species included in 
Table I may be found on white clover, which was abun- 
dant at Douglas Lake, the place of pupation of these 
species was tested in the following manner. A mass of 
the flowers of white clover was collected. The flowers 
were gently squeezed for some time to drive out all the 
adults. They were then placed in a vessel under cover. 
After two days, when the flowers were thoroughly dried, 
they were again gently crushed to make sure that all 
adults were driven out. At intervals from one to two 
weeks afterward, 15 adult thrips appeared on the inside 
of the glass cover. These were of three species, Euthrips 
tritici, Thrips tabaci and Anthothrips niger. 

I have also frequently observed the pupaB of Antho- 
thrips verbasci in mullein spikes, those of Sericothrips 
cingulatus on white clover, the pupa of Trichothrips tri- 
dentatus under the bark of the white oak, where the larvae 
and adults live, and that of an undescribed species on 
willow galls along with larvae of the same species. I 
judge from these observations that the majority of thrips 
pupate on the plants on which the larvae live, and that 
their rarity in collections is due merely to concealment 
and sluggish habits. 

Discussion of the Results in Relation to the Life 

Cycle 
From the data in Table I and the observations given 
above it is evident that there is considerable diversity in 
different species with regard to the life cycle, and diver- 
sity within the same species at different times or in 
different regions. First, as regards the mode of passing 
the winter, it would seem that in Euthrips tritici only the 
females survive that season. The reason for so believing 



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No. 568] BIOLOGY OF THE THTSANOPTERA 243 

is that males could not be found in the spnng until the 
females had been active long enough to have produced 
one generation of offspring. Males occur late in autumn, 
but must perish before the end of winter. Likewise, 
neither eggs nor larvae live over winter, or larv® would 
appear earlier in spring. In Thrips physopus, on the 
other hand, males were found as early as the females; 
hence, in the absence of any collection earlier than May 
22, and in ignorance of the time required for develop- 
ment, I should assume that both sexes survive the winter. 
Both sexes of Anthothrips verhasci have been seen on 
dead mulleins in winter. 

In species, like Euthrips tritici, whose males do not 
survive the winter, if fertilization of the early spring 
females takes place at all, it must occur in the fall. I do 
not regard my breeding experiments as proof of par- 
thenogenesis in this species, but it is by no means improb- 
able that parthenogenesis occurs. More rigorous experi- 
ments are needed. 

As regards the mode of reproduction during the rest of 
the year, there is nothing in the sex ratio, as given in 
Table I, to suggest an alternating cycle in Euthrips tri- 
tici. In other species, it would be possible to interpret 
certain facts to mean that an alternation of partheno- 
genesis and sexual reproduction occurs, or did once 
occur. There is a well-marked increase in the proportion 
of males in Anaphothrips striatus, for example, in Au- 
gust. This is a particularly interesting species. Hinds 
(1902) saw only the female of this species, though he 
mounted and examined over a thousand specimens, and 
he bred it parthenogenetically in the laboratory for 
months. What purported to be the male was described 
by Gary (1902), from Maine, but the specimens described 
were evidently those of another species. The first males 
ever recorded were described by ShuU (1909), two speci- 
mens among probably two hundred females. It is re- 
markable, therefore, that in the vicinity of Douglas Lake 
there should be nearly 25 per cent, of males. Whether 



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24^ THE AMERICAN NATURALIST [Vol. XLVHI 

the presence of numerous males is dependent on climatic 
conditions, or whether it is a racial difference, there is at 
present no way of deciding. The weather was unusually 
cold during the summer in which these records were 
made, and it is desirable that the effect of temperature be 
experimentally determined. The presence of males in 
goodly numbers throughout the summer, the occurrence 
of copulation in nature, and the failure of an attempt to 
breed the species parthenogenetically, leave, as the only 
reason for suspecting that it may have been partheno- 
genetic at Douglas Lake, the fact that it is parthenoge- 
netic elsewhere. But if the species is parthenogenetic in 
one region and sexual in another, it is not diflScult to be- 
lieve that it may be both parthenogenetic and sexual in 
the same region. It is diflScult to decide whether the well- 
marked increase in the proportion of males in August 
and early September should be regarded as evidence of 
such an alternation, or as due to a period of cold weather 
or other climatic factor, or as a hereditary remnant of 
the sexual phase of an alternating cycle once possessed 
by the species. Only experiment, and perhaps cytological 
study, can decide this question. 

A similar but less marked increase in the number of 
males is seen in Anthothrips verhasci, also in August. In 
that month the proportion of males rose from about 20 
per cent, to 40, or even nearly 50 per cent. In this species 
the increase may be due to the late date at which the first 
brood of larvfiB becomes mature. The life history of this 
species is longer than that of most of the suborder Tere- 
brantia, and may appear to be still longer because ene- 
mies destroy many of the larger larvae. For these rea- 
sons, in the region of Douglas Lake, the first generation 
of larvae may not become mature until nearly August. If 
this assumption is correct, the proportion of males found 
prior to August is the proportion that survive the winter. 
This explanation receives support from the cytology of 
the germ cells. As stated above, there is a lagging chro- 
mosome in the spermatocyte divisions, which suggests 



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No. 668] BIOLOGY OF THE THTSANOPTERA 246 

the probability that there are two classes of sperm asso- 
ciated with sex, as in the bugs and many other animals, 
and that therefore the sexes should be approximately 
equal in numbers. The 40 to 50 per cent, of males in 
August accord fairly well with this explanation. 

This explanation would not, however, account for the 
increase in the number of males in late summer in a spe- 
cies whose life Tiistory is much shorter than that of 
Anthothrips verbasci. Thus, in Anaphothrips striatus, 
Hinds states that the entire life history is passed through 
in 12 to 30 days. Even in a cold season, such as that of 
1912 at Douglas Lake, therefore, the life history can not 
have been so long that the first adults would emerge in 
the middle of August. The increase in the number of 
males of Anaphothrips in August and September is not 
to be explained, therefore, as due to the first appearance 
of a new brood at that time. 

Thrips tabaci likewise affords interesting, even if mea- 
ger, evidence regarding the seasonal occurrence of males. 
In this species males are exceedingly rare. Hinds (1902) 
redescribed the male in quotation marks, from which it 
is to be inferred that he did not have specimens. In my 
own collecting, though the females were quite common, I 
never saw a male until the summer of 1912. Then two 
specimens were taken September 2, as shown in Table I* 
These irregularly occurring males can hardly be func- 
tional, so that Thrips tabaci is still probably to be re- 
garded as wholly parthenogenetic. But their appearance 
in late summer may be the vestige of a former sexual 
phase, and may be caused now, as the sexual phase prob- 
ably was in part formerly caused, by climatic conditions. 

Chirothrips manicatus presented, at Douglas Lake, an 
anomalous condition. As shown in Table I, and stated 
more explicitly above, females were abundant in a given 
small area early in July, but practically no males were 
pr^ent. Then, so far as I could determine by painstak- 
ing collections, the females disappeared ; almost no adults 
of either sex, and not many larvae, were to be found. Two 



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246 THE AMERICAN NATURALIST [Vol. XLVIH 

weeks later, however, males were found in the same area 
in large numbers. As these males were wingless, they 
had probably not immigrated. The only other explana- 
tion that occurs to me is that the larvae were present in 
considerable numbers at the time of the earlier collec- 
tions, but in the flowers, not among the spikelets of the 
timothy, so that I did not discover them; and that the 
female larvae reached maturity much earlier than the 
males. In any case, it is diflScult to see how the males can 
have been functional, when the two sexes occurred at dif- 
ferent times. If such conditions recur frequently, Chiro- 
thrips manicatus, eVen though it produces many males, 
must be parthenogenetic. 

SUMMABY 

The principal conclusions reached in the second "part of 
this work may be stated as follows : 

Some species of Thysanoptera pass through the winter 
in both sexes, in others the males perish. In none of 
those studied does the egg or larva live over winter. 

Pupation of most of the species of Thysanoptera stud- 
ied occurs on the food plants where the larvae live, not- 
withstanding that the pupae seldom appear in collections. 

From the determination of the sex ratio, Euthrips 
tritici shows no indication of an alternating life cycle. It 
is probably sexual throughout the active season, though 
this is not proven. 

Chirothrips manicatus occurred abundantly in both 
sexes, but the two sexes appeared at different seasons. 
The explanation of this phenomenon is doubtful. 

An increase in the number of males in Anthothrips 
verbasci in late summer may be explained as due to the 
great length of the life history and to selective mortality 
during the winter, without assuming an alternating life 
cycle. 

Anaphothrips striatus, a species which has hitherto 
been known almost wholly in the female sex, produced 
about 25 per cent, of males at Douglas Lake. This may 



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No. 568] BIOLOGY OF THE THYSANOPTERA 247 

be due either to climatic conditions or to racial differ- 
ences. Sexnal reproduction was not wholly proven, but 
seems probable. An increase in the number of males in 
late summer in this species and in Thrips tabaci might be 
interpreted as indicating a sexual phase, or the vestiges 
of a sexual phase that existed in the species formerly, 
Jordan's belief in an alternating life cycle, which was 
rejected by Uzel, thus receives some measure of jus- 
tification. 

BIBLIOGRAPHY 
Gary, L. B. 1902. The grass thrips (Anaphothrips striata Osborn). Maine 

Agr. Exp. Station, Bull. 83, June, pp. 51-82. 
Jones, P. B. 1912. Some new California and Georgia Thysanoptera. U. S. 

Dept. Agr., Bur. Ent., Tech. Ser. No. 23, Part 1, 24 pp., 7 pis. 
Jordan, K. 1888. Anatomie und Biologie der Phjsapoda. Zeit, iviss, 

ZooL, Vol. 47, pp. 541-620. 
Hinds, W. E. 1902. Contribution to a monograph of the insects of the 

order Thysanoptera inhabiting North America. Proc. U, 8, Nat. 

Museum, Vol. 26, No. 1310, December 20, pp. 79-242. 
Maupas, E. 1890. Sur la fdcondation de THydatina senta Ehr. Comp, 

Bend. Acad. 8ci. Paris, Tome 111, pp. 505-507. 
Moulton, Dudley. 1911. Synopsis, catalog and bibliography of North 

American Thysanoptera. U. S, Dept. Agr., Bur. Ent., Tech. Ser. No. 

21, 56 pp. 
1912. Papers on deciduous fruit insects and insecticides. IV. The pear 

thrips and its control. U. S. Dept. Agr., Bur. Ent., Bull. 80, Part IV, 

pp. 51-66. 
Shelf ord, V. E. 1911. Physiological animal geography. Joum. Morph., 

Vol. 22, No. 3, September, pp. 551-618. 
Shull, A. F. 1909. Some apparently new Thysanoptera from Michigan. 

Entom. News, Vol. 20, No. 5, pp. 220-228. 
1911. A biological survey of the sand dune region on the south shore of 

Saginaw Bay, Michigan. Thysanoptera and Orthoptera. Mich. Geol. 

and Biol. Survey, Pub. 4, Biol. Ser. 2, pp. 177-231. 
Uzel, H. 1895. Monographie der Ordnung Thysanoptera. KOniggratz, 

privately published, 482 pp., 10 pis. 



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SHORTER ARTICLES AND DISCUSSION 

BARRIERS TO DISTRIBUTION AS REGARDS 
BIRDS AND MAMMALS 

The geographical range of any species of animal may be 
likened to a reservoir of water in a mountain canyon. The con- 
fining walls are of varying nature. A concrete dam, absolutely 
impervious, may retain the water at one end. Along either side 
the basin's walls differ in consistency from place to place. The 
substratum varies in porosity, at some points being impervious 
like the dam, at others permitting of seepage of water to a greater 
or less distance from the main volume. The water continually 
presses against its basin walls, as if seeking to enlarge its area. 
And it may succeed in escaping, by slow seepage through such 
portions of its barrier as are pervious or soluble, or by free flow 
through a gap in the walls, if such ofiPers. The area occupied 
by the water will extend itself most rapidly along the lines of 
least resistance. 

Every species has a center or centers of abundance in which 
favoring conditions usually give rise to a rate of reproduction 
more than sufficient to keep the critical area stocked. A tendency 
to occupy a larger space results, because of competition within the 
species: individuals and descent-lines multiply and travel radi- 
ally, extending those portions of the frontier where least resist- 
ance is offered. Such radial dispersal takes place slowly in some 
directions, more rapidly in others, according to the degree of 
passability of the opposing barriers. These barriers consist of 
any sort of conditions less favorable to the existence of the 
species than those in the center of abundance. 

Theoretically, sooner or later and in all directions, every 
species is absolutely stopped. But as a matter of undoubted 
fact most barriers are continually shifting, and the adaptability 
of the animals themselves may be also undergoing continual 
modification ; so that perfect adjustment is beyond the limits of 
possibility so long as topography and climate keep changing. 
The ranges of species may thus be constantly shifting. Descent- 
lines may move about repeatedly over the same general region, 
like sparks in the soot on the back of a brick fireplace. 

Yet, in all of our studies, of but a few years' duration, the 

248 



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Na 568] SHORTER ARTICLES AND DISCUSSION 249 

time element is reduced almost to a negligible quantity, and we 
may look upon the areas occupied by each species as, for the 
time of our observation, fixed. We are thus enabled to compare 
one with another, and because of the large number of the species, 
we can infer a good deal as to the nature of barriers in general, 
at least as regards birds and mammals. It is even conceivable 
that ; with sufScient refinement in methods, the inquirer might in 
time find himself able, from a comparative study of the ranges 
of rodents, for example, to establish the identity of all of the 
external factors which have to do with the persistence of each of 
the species; in other words to analyze the ** environmental com-, 
plex'' into its uttermost elements — as regards the existing species 
of rodents in their recent development. 

The most obvious kind of barrier to distribution is that con- 
sisting of any sort of physical, or mechanical, obstruction. Such 
obstruction aflFects directly the individuals of a species en- 
countering it, either by stopping their advance or by destroying 
outright such as attempt to cross it. As barriers of this nature, 
are to be cited land in the case of purely aquatic mammals, and 
bodies of water to purely terrestrial, especially xerophilous, 
mammals. In each case the width of the barrier has to do with 
the degree of impassability. Oceans and continents are most 
perfect, and aflfect a large proportion of the species. The com- 
paratively narrow Colorado River is a barrier of the first rank, 
but only to a certain few desert rodents. Mechanical barriers, 
where they exist at all, are clearly recognizable. 

It is to be observed, however, upon considering the birds and 
mammals of a whole continent, that by far the greater number 
of species are delimited in range without any reference to actual 
land and water boundaries ; more explicitly, their ranges fall far 
short of coast lines. The barriers here concerned are intangible, 
but nevertheless powerful. By their action the spread of species, 
genera and families is held in check as surely as by any tangible 
obstruction. 

By these invisible barriers the individual may not necessarily 
be stopped at all, as with animals of free locomotion; but the 
species is affected. For example, the mocking bird in its Cali- 
fomian distribution is closely confined to those parts of the state 
IKMSsessing certain definite climatic features; but vagrant indi- 
viduals, especially in autumn, occur far beyond the limits of 
these restrictive conditions. Carnivorous mammals are well 



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250 THE AMERICAN NATURALIST [Vol. XLVIII 

known to be subject to sporadic wanderings on the part of indi- 
viduals, but the species is kept in set bounds by some potent but 
invisible set of factors. The very fact that individuals are quite 
capable of temporarily transgressing these bounds and yet do 
not overstep them en masse emphasizes all the more the remark- 
able potency of this category of barriers as regards species and 
higher groups. 

Our geographic studies lead us to designate among these rela- 
tively intangible barriers: (1) increase or decrease in prevailing 
temperature beyond certain critical limits, according to the species 
concerned; (2) increase or decrease in prevailing atmospheric 
humidity beyond certain limits; (3) modification in food-supply 
and appropriate breeding and foraging ground. The limits set 
by each of these factors will vary with the physiological pecul- 
iarities of the organism considered ; in other words the inherent 
structural equipment of each animal figures importantly. In 
these three sorts of barriers will be recognized what have been 
called ''zonal/' ''faunal" and ''msociationaV delimitation, each 
of which I will now try to define. 

Two schools of f aunistic students are represented among Amer- 
ican zoo-geographic writers of the present day. One, of which 
C. H. Merriam is the most prominent exponent, sees in tempera- 
ture the chief cause controlling distribution, and deals with the 
ranges of species in terms of **life zones.'' The other school, of 
which C. C. Adams, A. G. Ruthven and Spencer Trotter are 
active advocates, assigns to temperature but a minor role, look- 
ing rather to a composite control, of many factors, resulting in 
ecologic ** associations," of which plants are essential elements, 
and which are to be further explained on historical grounds. 
The two sets of areas thus defined do not by any means corre- 
spond. Yet the reviewer can not fail to note, here and there, 
places where boundaries coincide, and such coincidences are so 
frequent as to be suggestive of real concordance in some signifi- 
cant manner. Is it not probable that both schools are approxi- 
mately correct, the difference in mode of treatment being due to 
different weights given the different kinds of evidence, or, in 
other words, to difference in perspective? 

Every animal is believed to be limited in distribution zonally 
by greater or less degree of temperature, more particularly by 
that of the reproductive season. When a number of animals 
(always in company with many plants similarly restricted) 



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No. 568] SHORTER ARTICLES AND DISCUSSION 251 

approximately agree in such limitation they are said to occupy 
the same life zone. 

The observation of this category of distributional delimita- 
tion is particularly easy in an area of great altitudinal diversity 
like that comprised in the southwestern United States. The 
writer is led to wonder if those authors who minimize the impor- 
tance of temperature have ever been privileged to travel exten- 
sively, and carry on field studies, outside of the relatively uni- 
form eastern half of North America ! 

Study of any area which varies widely in altitude and hence 
provides readily appreciable diflEerences in daily temperature 
from place to place brings conviction of the very great eflEective- 
ness of temperature in delimiting the ranges of nearly all species 
of animals as well as of plants. Particular attention may be 
called to the pertinent results of Merriam's survey of Mount 
Shasta. 

But temperature is not to be considered the only delimiting 
factor of environment, though its possible overemphasis by the 
Merriam school seems to have led some other persons to believe 
that this view is held. In fact it becomes evident, after a con- 
sideration of appropriate data, that very many species are kept 
within geographic bounds in certain directions only by an in- 
creasing or decreasing degree of atmospheric humidity. By 
plotting the ranges of many animals as well as of plants coin- 
cidence in this regard is found in so many cases as to warrant 
the recognition of a number of **faunal areas" — on the causa- 
tive basis of relative uniformity in humidity. It is probable that 
every species is affected by both orders of geographic control. 

The reader may enquire as to the grounds for employing the 
widely used terms zone and fauna in the restricted sense here 
prescribed. In reply, it may be said that this is not an inno- 
vation, but is an adoption of a usage which has come about his- 
torically among a certain group of workers in the geography of 
vertebrate animals in North America. The writer recognizes the 
fanlt in imposing restricted meanings upon old terms, but he 
also hesitates at coining new words. 

As to which is the more important, assembled data seem to- 
show that more genera and higher groups are delimited by zonal 
bomidaries than by faunal boundaries. The arresting power of 
temperature barriers would therefore seem to be relatively the 
greater. 



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252 THE AMERICAN NATURALIST [Vol. XLVni 

In the third category of distributional control there is a con- 
spicuous association of the majority of so-called adaptive struc- 
tures of animals (often of high taxonomic value) with certain 
mechanical, or physical, features of their environment An 
animal may thus intimately depend upon certain inorganic or 
organic peculiarities, or both, of a given area, and be unable to 
maintain existence beyond the limits of occurrence of those 
features of the environment. Tracts of relatively uniform en- 
vironmental conditions, including their inanimate as well as 
living elements, are here called associations. 

After a consideration of all the birds and mammals occurring 
both within the state of California and elsewhere as far as the 
writer's knowledge goes, associational restriction appears to be 
governed by the following three factors, of relative importance 
in the order named. 

1. Kind of food-supply afforded, with regard to the inherent 
structural powers of each of the animals concerned to make it 
available. 

2. Presence of safe breeding places, adapted to the varying 
needs of the animals, in other words depending upon the respect- 
ive inherent powers of construction, defence and concealment 
in each species concerned. 

3. Presence of places of temporary refuge for individuals, 
during daytime or nighttime, or, while foraging, when hard- 
pressed by predatory enemies, again correlated with the respec- 
tive inherent powers of defence and concealment of each species 
involved. 

It is believed that the geographical distribution of any animal 
is correctly diagnosed in terms of each of the three main group- 
ings here suggested. In other words an animal belongs simul- 
taneously to one or more zones, to one or more faunas, and to 
one or more associations. No one of these groupings can be 
stated in terms of the other, any more than a person can com- 
pute liquids by candle-power, or weight in miles. The constit- 
uent species within each of these groupings always belong to 
the other two. To illustrate: the southern white-headed wood- 
pecker inhabits the coniferous forest association of the San 
Bernardino fauna of the Transition zone; the Abert towhee be- 
longs to the mesquite and the quail-brush associations of the CJolo- 
rado Desert fauna, of the Lower Sonoran zone ; the Pacific shrew 
belongs to the upland riparian association of the northern coast 
redwood fauna of the Transition and Boreal zones. 



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No. 568] SHORTER ARTICLES AND DISCUSSION 268 

Classification of Barriers to Species as Regards 
Birds and Mammals 
Barriers: 

A, Intangible. 

(a') Zonal (by temperature). 

(6') Faunal (by atmospheric humidity). 

(c') Afisociational. 

(1) By food supply. 

(2) By breeding places. 

(3) By temporary refuges. 

(Each of these three with regard to the inher- 
ent structural characters of each species 
concerned.) 

B. Tangible (mechanical). 

(a") Land to aquatic species. 

(6") Bodies or streams of water to terrestrial species. 

The above categories are believed to include all the factors 
commonly involved in checking the spread of species of birds and 
mammals. It is possible that inter-specific competition may 
sometimes occur where associational homologues meet. But even 
here it becomes a matter of relative associational fitness which 
determines supremacy and consequent ultimate limits of inva- 
sion of the forms concerned. 

A mountain range, mechanically speaking, is no barrier at all, 
per se, as frequently alleged. Only as it involves zonal or faunal 
barriers does it aflfect distribution. The same is true of a valley 
or a desert. 

As far as contemplation of cases has gone, the writer's experi- 
ence has led him to believe that the outlines of the ranges of all 
birds and mammals may be accounted for by one or more of the 
factors indicated in the analysis here presented. And as de- 
tailed knowledge of the facts of geographical distribution accu- 
mulates, the delimiting factors become more and more readily 
detectable. By such a study, of comparative distribution, it 
seems possible that the ranges of birds and mammals may become 
subject to satisfactory explanation. 

When considered in its historical bearing, the problem of 
barriers concerns itself intimately with the origin of species. It 
is believed by the writer that only through the agency of barriers 
is the multiplication of species, in birds and mammals, brought 
about. 



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264 THE AMERICAN NATURALIST [Vol. XLVIH 

The present contribution is abbreviated from-a general discus- 
sion of certain distributional problems which forms part of a 
paper to appear from the University of California press and 
which treats in detail of the birds and mammals of the lower 
Colorado Valley, in California and Arizona. 

Joseph Gbinnell 
Museum or Vertebrate Zoolooy, 
University op Calitc>rnia 

YELLOW VARIETIES OF RATS 

In a recent number of the Naturalist I described a yellow 
variety of the common rat {Mus norvegicus) which in recent 
years made its appearance in England and is now a recognized 
variety among fanciers. Dr. John C. Phillips and Professor L. 
J. Cole have both called my attention to a fact which I had over- 
looked; namely, the occurrence of a yellow variety in another 
species of rat {Mus rattus) . Bonhote described the occurrence of 
this variety in Egypt in 1910 and has since found by experiment 
(1912) that the yellow variation of Mus rattics is recessive in 
heredity precisely as it is in Mus norvegicus. The fact that the 
yellow variation in mice is dominant in heredity, but can not be 
obtained in a homozygous condition, stands, therefore, as a phe- 
nomenon all the more singular and striking. 

W. E. Castue. 

BussET Institution, 
March 3, 1914. 



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NOTES AND LITERATUEE 

HEREDITY AND ''THE INFLUENCE OP 
MONARCHS'' 

In **The Influence of Monarchs'* (xiii and 422 pp., 1913, The 
Maemillan Co., New York, $2.00) Dr. Frederick Adams Woods 
makes a second and firmer step along the path entered on with his 
interesting ''Mental and Moral Heredity in Royalty" published 
in 1906. Dr. Woods's goal in beginning and continuing his an- 
alysis of the character of royalties and the circumstances of their 
reigns is one probably not immediately to be reached but also 
probably one not impossible of attainment. It is indeed not one 
goal that he has before him, but two, the ways to which lie close 
together and parallel. One is the establishing of a new science of 
history to be called historiometry ; the other is the making ap- 
parent of the dominan'ce of heredity over environment in deter- 
mining human fate. 

That the methods and even the aims of most historical study 
are not satisfying to all historical students is made obvious by 
the constant complaining of historians to and of each other. 
There are two conspicuous groups of these protestants, one de- 
manding more interest, more imagination, a more literary treat- 
ment of historical fact, and the other demanding a more signifi- 
cant, more inductive, more scientific treatment. The former 
wants more "humanity,'' the latter more biology, in history. 
Dr. Woods is of the latter group. 

But Dr. Woods is not primarily of any historical camp. He is 
biologist, especially evolutionist and student of heredity. How- 
ever, he marches very boldly into the ranks of the students of his- 
torical human history — to distinguish thus the last few thousand 
years of human history from the earlier many thousand years 
of it — with the new methods and results of his historiometry, 
just as Pearson, several years ago, invaded the biological camp 
with his biometry. Something of historiometry in history there 
has always been, just as there has always been something of 
biometry in biology. But these reformers want to make history 
and biology wholly, or, at least, most importantly, sciences of 
measure. And each of them finds that his use of measure in them 
leads him to discover that the facts that he is measuring offer, in 
the new significance they are thus made to yield, a special argu- 
ment for some particular one of the major factors in evolution. 

255 



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256 TRE AMEBIC AN NATURALIST [Vol. XLVIH 

Biometry emphasizes the enormous importance and significance of 
variation in all living things ; historiometry reveals the enormous 
importance of heredity in human life and the affairs of society. 

After an introductory chapter stating the need of a new inter- 
pretation of history and of new methods of getting at this inter- 
pretation, and a following general chapter further elaborating 
and expanding his views concerning ''the philosophy of history 
and historiometry,'' Dr. Woods plunges into a series of compact 
histories of France, Castile, Aragon, United Spain, Portugal, The 
Netherlands, Denmark, Sweden, Russia, Prussia, Austria, Turkey, 
Scotland and England. In each of these he presents a swift sum- 
mary of the economic and political conditions (success in wars, 
increase in territory and prestige, prosperity, advance, failures in 
war, loss of prestige, poverty, retrogression) of these nations in 
the various reigns of a period of about 500 years for each country, 
together with a statement of the personal traits of each monarch. 
In all, three hundred and sixty-eight monarchs, regents or other 
rulers, royal or non-royal, and correspondingly, three hundred 
and sixty-eight sets, or periods, of national conditions, are pre- 
sented. 

Prom these data is derived the very positive and important 
conclusion that the dominant causal influence in determining the 
character of national, political and economic conditions has been 
the personality of the monarchs, and that the prime determinant 
of this personality is heredity and not environment. 

A host of possible criticisms and objections to the method, its 
results and their interpretation, leaps into every one's mind. 
Well, they are all — or all that I have so far been able to formu- 
late — ^anticipated, and ingeniously, and usually convincingly, 
answered. At least they are anticipated and discussed. In this 
the book reminds one of Darwin's ** Origin of Species." 

To all who have read ** Heredity in Royalty" this new book of 
Dr. Woods will need no recommendation of its interest and im- 
portance. To those who have not, and are interested either as 
historian, biologist, or natural philosopher in human history and 
the bionomic factors that control it, *'The Influence of Monarchs" 
may be strongly recommended as an original and very suggestive 
treatment of the subject. To students of heredity the book is a 
necessary library addition. 

V. L. K 

Stanford Univkesitt, 
California 



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The American Naturalist 

A MoatUr Jomul ••uUkli«d in 1867, D«TOtod Id th« AdTUie«neiit of th« Biologieal ScImcm 


CONTENTS OF THE OCTOBER NUMBER 

▲ Contribution towtidt an Analysis of ibe Problem 
of Inbroedinf . Dr. Baymond PcarL 

Tbo Inhtfltanee of Coat Color in Honet. Prof eMor 
W.8.Andenon. 

The Variations in the Nomberof Yertcbre and Van- 
tral Scntas in Two Snakes of the Qenos Beffina. 
Professor Alexander G. Rnthyen and Crystal 
Thompson. 

Shorter Articles and Beporta : The Bimnltaneoas 
Modifloation of Distinct MendeUan Factors: .Pro- 
fessor B. A. Smerson. TheFoorthlnternatiGnal 
Oenetie Conferenee : Dr. Frank M. Snrfaoe. 


CONTENTS OF THE NOVBMBEII NUMBER 
The Effect on the Offspring of Intoslcatinc the Male 

Supplementary Studies on the I>ifflerentlal Mortalitgr 
with respect to Seed Weight in theQermlnatioB 
of Garden Beans, Dr. J. Arthur Harris. 

Shorter Arttdes and Discussion : Bedprocal Crosm 
hetween Beere's Pheasant and the Common 
Ringneck Pheasant producing Unlike Hyhrids. 
John C. Phillips. 


CONTENTS OF THE DECEMBER NUMBER 

The Fixation of Character in Orranisms. By Edward 

Sinsott. 
Inheritance of Left-handedness. Professor Francis 

Bamaley. 
Supplementary Stndies on the DUTerential MortaUty 

with Bespect to Seed Weight in the GerminaUon 

•f Garden Beans, n. Dr. J. Arthur Harris. 
Shorter Articles and Discussion : A Cross InTolTing 

Four Pairs of Mendelian Characters in liiee. C. 

CLlttte, J. C.Phillips. 
Index to Volume ZLVIL 


OONTENT8 OP THE JANUARY NUMBER 
A Genetic Analysis of the Changes produced hj 

fessor E. M. East and H. K. Hayes. 
Gynandromorphous Ants, described during the De* 

cade. lMa-1918. Professor William Ifdrton 

Wheeler. 
Shorter Articles and Discussion : On the Seeults of 

Inbreeding a Mendelian Population— A OoRee» 

tion and Extension of PreTlous Condurioos. 

Dr. Raymond Peail-^Isolation and Belaotktt 

alUed in Pnndple. Dr. John T. Qultek. 


CONTENTS OF THE FEBRUARY NUMBER 

Some New Varieties of Bats and Guinea-pifs and their 

Belations to Problems of Color Inheritance. Pro- 
fessor W. B. Castle. 
«< Dominant" and *« BecessiTe" Spottlnff in Mice. C. 

C. Little. ^^ 
On Difterential MortaUty with respect to Seed Weight 

occurring in Field Cultures of Pisum sativum. 

Dr. J. Arthur Harris. 
The Inheritance of a Beeurrlng Somatio Variation 

In Variegated Ears of Maise. Professor B. A. 

Emerson. 
Bestoration of Edaphosaurus crudger Cope. Pro- 

fessor E. C. Case. 
Shorter Articles and Discussion : Humidity— a 

Neglected Factor in EuTironmental Work. Dr. 

Frank B. Lutz. 


CONTENTS OF THE MARCH NUMBER 

Asa C. Chandler. 
Biology of the Thysanoptera. Dr. A. Franklin BbnU. 
Shorter Articles and Correspondence : The Endemic 

CockereU. 
Notes and Literature : Swingle on VarlatloB in li 
Citrus Hybrids and the Thawy of Zygotasls. 
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258 THE AMERICAN NATURALIST [Vol. XLVIII 

lated from the rest of the individuals comprising the par- 
ticular species represented by it. This brings about cer- 
tain striking conditions of abundant small variation and 
subspecific (or intraspecific) distinction, which, however, 
because of the general similarity of habitat, food and 
habit, do not tend to grow rapidly into large (specific, 
generic, family) diflFerences. The hundred or more species 
of Mallophaga so far recorded from mammals have, until 
very recently, all been ascribed to two genera, of which one 
included nearly nine tenths of the total number of kinds. 
There has been made a beginning — and not a particularly 
convincing one — at breaking up this inclusive genus 
(Trichodectes). It is a movement suggested more by the 
needs of convenience than the needs of expressing a bio- 
logical situation. Similarly, although not representing 
so extreme a condition of likeness, the Anoplura, also 
including about a hundred parasite species (occurring 
only on mammals) have been, until recently, divided into 
but half a dozen genera, with the great majority of the 
species included in one. Certain aberrant forms found 
on man, the monkeys, the elephant, and on seals and 
walruses have always made necessary the recognition of 
four or five quite distinct genera. Attempts, however, are 
now being made to break up the unwieldly genus Hcema' 
topinus. 

As this paper is, in eflFect, a continuation of my paper 
on ''Distribution and Species-forming of Ecto-parasites'' 
published in The American Naturalist in March, 1913, 
which devoted itself to a consideration of the Mallophaga 
(some 1,400 species as so far known) found on birds, and 
to the problems presented by their conditions of life and 
their host and geographic distribution, I can dispense 
with any further account of the special biology of these 
parasites by referring the interested reader to this 
former paper. In it I have set out rather fully the spe- 
cial structural and habit features of the Mallophaga. 
Except that the Anoplura 'take blood, rather than 
feathers and hair, for food, and have specially modified 



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No. 569] ECTOPARASITES OF MAMMALS 259 

mouth parts to do it with, and are perhaps even more 
specialized in their physiological adaptations to their 
host than the biting lice, most of the general remarks 
made concerning the Mallophaga will apply to the suck- 
ing lice also. 

In their peculiar special relations to their hosts as per- 
manent ectoparasites on them, wingless, and reluctant to 
migrate even with opportunity, and so fitted physiologi- 
cally to their parasitic life that they can not live for more 
than a few hours (or, at most, and exceptionally, days) 
off the bodies of their hosts, the Anoplura and Mallophaga 
are alike. And hence the conditions and problems of 
their distribution and species-forming are practically the 
same for the two groups. 

The thesis that I have maintained, on a basis of the 
conditions presented by the bird-infesting Mallophaga, 
I now wish to test by the conditions presented by the 
mammal-infesting Mallophaga and Anoplura. This thesis 
is, in fewest words, that the host distribution of these 
wingless permanent ectoparasites is governed more by 
the genetic relationships of the hosts than by their geo- 
graphic range, or by any other ecologic conditions. The 
fact, proved by abundant cases, that two host species of 
wholly distinct geographic range and with no possible 
opportunity for contact such as would permit of the 
migration of wingless parasites from one to the other, 
may have, nevertheless, one or more parasitic species 
common to them both, is associated almost always with 
the further fact that these common hosts are closely 
related genetically. They are most often of the same 
genus or of closely allied genera; they are almost cer- 
tainly always of the same subfamily or family. The ex- 
planation for the possibility and the reality of this inter- 
esting host distribution I find in the hypothesis that the 
common parasite species has persisted unchanged from 
a common ancestor of the now divergent but allied host 
kinds. 

Also, if it be true that genetic relationship is the deter- 



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260 THE AMERICAN NATURALIST [Vol. XL VIII 

mining factor in accounting for the host distribution of 
the parasites, then it is also true that the distribution of 
the parasites will indicate in some measure the genetic 
relationships of the hosts, and that occasional aid in 
determining the genetic affinities of birds and mammals 
of doubtful relationships may be had from a study of 
their parasitic fauna. In my paper already referred to 
I have pointed out some suggestive cases of this sort in 
connection with the birds and their parasites. 

In examining the conditions existing among the mam- 
mals and their Mallophagan and Anopluran fauna, the 
first necessity was the compilation of a complete record 
or catalogue of mammalian hosts and their parasites, 
together with the record of the actual locality of each 
finding of parasites, together with a general record of the 
geographic range of all the various hosts. This cata- 
logue, or set of records, I have now completed, and 
despite its meagerness compared with the similar cata- 
logue of the bird hosts and their Mallophagan parasites 
from which the notes for the former paper were drawn, 
it contains enough records of interest to make worth 
while a preliminary report on the condition obtaining 
among the mammals and their parasites. 

It is unfortunate that, although there are nearly one 
fourth as many mammal species as bird kinds, only about 
one hundred mammals figure in the Mallophagan host 
list, while Mallophagan parasites have been taken from 
over eleven hundred bird species. Also, only one hun- 
dred different Mallophaga have been taken from mam- 
mals, while about fourteen hundred have been taken 
from birds. Of the Anoplura, which are found only on 
mammals, records have been made from about one hun- 
dred host species, these records referring to just about 
the same number of Anopluran kinds. Thus the mam- 
malian host catalogue with its list of parasites is a short 
one ; as far as it goes, however, it is thoroughly interest- 
ing and suggestive. 

In working up the records I have used Trouessart's 



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No. 569] ECTOPARASITES OF MAMMALS 261 

'^Catalogus Mammalium" as an authority for the synon- 
omy of the hosts, and my own judgment, based on a con- 
siderable personal knowledge of the parasites and on a 
careful consideration of all the more intelligible litera- 
ture of the two groups, as a last court for the synonomy 
of the Mallophaga and Anoplura species. The synonomy 
of the parasites I have, however, not pushed far. 

With so much of introduction and explanation we may 
come to a swift resume of the results of a scrutiny of 
these records, proceeding by sequence of the mammalian 
orders, and referring to either or both groups of para- 
sites as they may happen to be represented in the para- 
site records of the successive host groups. 

II 

The Marsupialia are represented in the host list by 
half a dozen species of kangaroos and wallabies (family 
Macropidae) all from Australia, and a wombat, Phasco- 
lomys ur sinus (family PhalangeridaB), from Tasmania 
(also S. Australia?). From all of these hosts only Mallo- 
phaga are recorded, no Anoplura having yet been taken 
from a marsupial. The six species of kangaroos repre- 
sent three genera (Macropus, Petrogale and ^prym- 
nus), and their Mallophaga are of seven species, repre- 
senting four genera. Four of the species belong to the 
genus Boopia, and I strongly suspect are not all different. 
In addition there is one Trichodectes, from Petrogale 
penicillata, one Latumcephalum, from ** wallabies,** and 
one Heterodoxus, which is recorded from Macropus 
giganteus in Australia as well as from the same host in 
the Jardin des Plantes, Paris. It is also recorded from 
an undetermined wallaby in Victoria and one in Queens- 
land, as well as appearing in three other records from 
** kangaroo'* or ** wallaby** from Australia. The para- 
site of the wombat is a species of Boopia, and it has been 
twice recorded from the same host. It is interesting that 
the kangaroo in the Jardin des Plantes harbored, even 
after some period of captivity, only its own proper para- 



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262 THE AMEBIC AN NATURALIST [Vol. XL VIII 

sites without accepting new ones from its many, various 
and closely pressing neighbors. 

Of the four Mallophagan genera found on the kanga- 
roo, three, namely, Boopia, Latumcephalum and Hetero- 
doxus^ are peculiar to them. The third genus, Tricho- 
dectes, is represented by but a single species which has 
been recorded but once. This is the common Mallophagan 
genus of mammals generally. The record is perhaps a 
good one, but its lack of confirmation by being unrepeated 
either for the same species or for any other species of 
Trichodectes, is suggestive. Heterodoxus, Latumcepha- 
lum and Boopia are two-clawed genera ; that is, they are 
Mallophagan forms which belong to a family all the other 
genera of which are confined to birds. The characteristic 
structural difference between the mammal-infesting 
Mallophaga and the bird-infesting species is the presence 
in the first group of a single claw on each tarsus, and in 
the second of two claws. This difference is plainly an 
adaptive one concerned with the fitting of the foot for 
the seizing of hairs and scrambling about among them, 
on the one hand, and the manipulation of feathers and 
moving about on them, on the other. In examining living 
specimens under the microscope the special use and fit- 
ness of the feet, in the one case adapted to hairs and in 
the other to feathers, is obvious. However, Heterodoxus, 
Latumcephalum and Boopia, and, in addition, perhaps 
one other doubtful genus, represented by one species, and 
perhaps two or three species of another two-clawed 
genus, constitute exceptions to the general rule. It is of 
decided interest to note that the only genera of two- 
clawed Mallophaga found exclusively on mamtnals are 
limited to the Marsupials. The antiquity and isolation of 

1 The single valid species of this genus — the two or three that have been 
named are undoubtedly all the same — ^has also been recorded from dogs 1 In 
fact specimens in my own collection were received with the record *'from 
Japanese dog. ' * And Enderlein has recorded it from a dog from China and 
Neumann from a dog from Formosa. Yet dogs ordinarily do not harbor 
this parasite, and kangaroos and wallabies do. It seems necessary to be- 
lieve that the dog host records indicate cases of straggling from kangaroos 
in zoological gardens or menageries. 



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No. 569] ECTOPARASITES OF MAMMALS 263 

this host group strongly suggests that the one-clawed con- 
dition common to all other mammal-infesting Mallophaga 
is a derivative from the original two-clawed condition 
characteristic of the parasites of birds and of these ancient 
manmials. The two-clawed condition is, of course, the one 
common to insects generally and is characteristic of the 
Atropids, in whom I am inclined to see the ancestors, or 
near-ancestors, of the Mallophaga. All of the Anoplura, 
it may be added, which are exclusively mammal-infesting, 
are one-clawed. 

In this connection the suggestiveness of the fact that 
in face of the examination of many specimens of half a 
dozen species of kangaroos and wallabies, no Anoplura 
have yet been found on the Marsupials, may be referred 
to. I am coming strongly to believe that there is no such 
wide ordinal separation of the Mallophaga and Anoplura 
as our clinging to the fetich of *' biting and sucking 
mouth-parts'' as basis for radical classificatory separation 
has led us to effect. I believe, with Mjoberg, that the two 
groups of parasites have a fairly near genealogical 
aflSnity, their differences, which are particularly those of 
mouth-parts, being adaptive rather than palingenetic in 
character. The Anoplura have gone on from the Psocid- 
Mallophagan condition to a more specialized parasitic 
habit, and are the extremes of a general line of ecto- 
parasitic evolution. The absence of sucking lice from the 
kangaroos may mean that the Marsupials are older than 
the Anoplura! No other considerable group of mam- 
mals, except certain families of strong-smelling Carni- 
vora, is free from the blood-sucking parasites. 

There are but two Edentates in the host list, one, the 
Cape Ant bear, Orycteropus afer (family Orycteropo- 
didae) of south and central Africa, harboring a sucking 
louse, of genus and species peculiar to it, and the other, 
the three-toed sloth, Brady pus tridactylus (family Brady- 
podidae) of eastern South America, harboring a Mallo- 
phagan of species peculiar to it but of the genus Gyropus 
which is the less scattered, although still rather catholic, 



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264 THE AMERICAN NATURALIST [Vol. XLVIH 

genus of the two large ones characteristic of the 
mammals. 

The large order Ungulata, with its nnmerons domesti- 
cated and semi-domesticated species, is a favorite host 
group with both Mallophaga and Anoplura. Altogether* 
about thirty Anoplura and two dozen Mallophagan spe- 
cies are recorded from fifty host species representing nine 
Ungulate families. 

The family Elephantidae is represented by the African 
and Indian elephants, recognized as distinct species of 
distinct geographic range. They both harbor a common 
Anopluran species, HcBmatomyzus elephantis, of species, 
genus and family peculiar to the elephants. Fahrenholz 
has given the varietal name sumatranus to specimens of 
these sucking lice taken from an Indian elephant in 
Sumatra. Records show that the parasites have been 
taken from their elephant hosts not only in Africa and 
Asia, but in various zoological gardens, as Paris, Ham- 
burg and Rotterdam. 

The small family of Hyracidae, or conies, is represented 
in the host list by two species and perhaps a third one, 
one of which, the Syrian coney of west and south Asia, 
harbors one Anopluran and one Mallophagan, while from 
the other, the Cape coney of South Africa, the same 
Anopluran species is recorded as well as another of the 
same genus. This record of a second species is from a 
coney in the London Zoological Gardens. From the pos- 
sible third species of Hyrax (taken in the African Congo 
and perhaps, but not probably, also a Cape coney), a 
second Mallophagan species is recorded of the same 
genus, Trichodectes, to which that of the Syrian coney 
belongs. 

In the family Equidae three species, the horse, the 
donkey and BurchelPs zebra, all suffer from the infesta- 
tion of a common Anopluran species, Hcematopinus asini. 
In addition, the horse and the zebra have a common 

2 The sjnoDomy in the parasite records, and indeed in the host records 
as well, is a vicious tangle. I have done the best I can, for the present. 



j 

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No. 569] ECTOPARASITES OF MAMMALS 265 

Mallophagan parasite, Trichodectes parumpilosus, while 
the horse and donkey have another common biting louse, 
Trichodectes pilosus. Two varieties of Trichodectes 
parumpilosus have been named by Piaget, one from the 
zebra and another from * kittle horses of Java/* 

The pigs (family SuidsB), of which three wild African 
species besides the familiar animal of the barnyard are 
fouBid in the host list, are infested by two (perhaps three) 
species of Anoplura and one (a not too certain record) 
Mallophagan. Hcematopinus suis is found on the domes- 
tic Sus all over the world, while Hcematopinus latus of 
Neumann, H. phocochoeri of Enderlein and H. peristictus 
of Kellogg and Paine, which are almost certainly all one 
species, are recorded from the wart hog, Phacochcerus 
cethiopicus from Nyasa-land, Africa, and probably also 
from another wart hog species from Africa, and the Red 
River hog, Potamochcerus chceropotamus from Nyasa- 
land, Africa. In addition Potamochcerus demunis (prob- 
ably), rfrom German east Africa, is credited by Stobbe 
with a Mallophagan parasite peculiar to it, Trichodectes 
vosseleri Stobbe. 

The peccary, Dicotyles tajacu (family Dicotylidae) of 
Central wAmerica and southwestern North America, has a 
Mallophagan species peculiar to it, belonging to the 
smaller of the two large Mallophagan genera, namely, 
Gyropus. 

The dromedary, of north Africa and western Asia, and 
the bactrian camel, of central Asia, harbor a common 
sucking louse, Hcematopinus cameli. A doubtful second 
species called H. tuherculatus (Neumann thinks it iden- 
tical with cameli) has been recorded from a dromedary 
imported from India into Australia. The ** South Amer- 
ican camel,*' the llama, harbors an Anopluran species 
peculiar to it, and two Mallophagan species, Trichodectes 
hreviceps Rudow and T. incequalemaculatus Piaget. Al- 
though Rudow's species are often suspect, I have just 
had his hreviceps from a llama of Peru (collector C. H. 



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266 THE AMERICAN NATURALIST [V0L.XLVIII 

T. Townsend). With these llama Mallophaga there is 
also a small Anopluran which I have not yet worked out. 

The family Cervidae is represented in the host list by 
about ten species. They are infested by three species of 
Anoplura, each peculiar to its host, and six species of 
Trichodectes (Mallophaga) of which T. tibialis is com- 
mon to the roe deer of Europe and Asia Minor, an 
African Capreolus, and our own black-tailed deer of the 
western states. Trichodectes longicornis is common to 
the red deer of Europe and Asia Minor and the fallow 
deer of south Europe, Asia Minor and north Africa. 

The giraffe (family Giraffidae) harbors a sucking louse, 
Linognathus brevicornis, peculiar to it. 

The great family Bovidse, with its many buffalo, buck, 
sheep, goat and antelope kinds, is represented in the host 
list by five or six species of Bos, four African bucks, 
three or four sheep, the ibex, chamois and two or three 
goats, and five or six antelopes, or gazelles. The domes- 
tic ox, Bos taurus, harbors three species of Anoplura and 
one Mallophagan. Curiously, none of these species is 
recorded from any other Bos. On the other hand, the 
zebu, the Indian buffalo, and the American bison all 
have the same Anopluran species (and no other, nor any 
Mallophagan), while the yak of central Asia and the 
Kaffir buffalo each have an Anopluran peculiar to it. 
The four species of African reedbucks and duikerboks 
have, according to the records, each a peculiar species of 
sucking louse. These records need scrutiny. One of 
them is my own, but I had to describe the species without 
seeing the types of the others. The domestic sheep 
carries two Anopluran species and one Mallophagan. 
The latter occurs also on at least two wild species of 
Ovis, one of west Africa and the other of north Africa. 
The fat-tailed sheep has a record from German south- 
west Africa of a Trichodectes of its own. 

The domestic goat harbors one Anopluran and at least 
one Mallophagan, the latter being common also to the 
Angora goat, the chamois, and a wild ( ?) goat of Guinea, 



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No. 569] ECTOPARASITES OF MAMMALS 267 

and a wild (?) goat of Java. A recent description of a 
second Mallophagan species from the domestic goat is 
not convincing. The chamois has also an Anoplnran, but 
one, so far, peculiar to it. Three species of Gazella (or 
Antilope) have three species of Trichodectes, of which 
one is common to two host species, one of Arabia and 
Syria and the other of north Africa and southwest Asia 
generally. This same Trichodectes is also recorded from 
the roan antelope, Hippotragus equinus, of east central 
and south Africa. One species of Gazella carries an 
Anopluran peculiar to it, as does also Tragelaphus grains 
of west Africa. 

The order Carnivora is represented in the host list by 
eight families and a total of fifty-four species. Only one 
species of Anopluran, the common sucking louse of the 
dog (not found yet even on the wolf or fox, both of which 
have other records) is recorded from a Carnivore, outside 
of the two families Trichechidae (walruses) and Phocidie 
(seals and sea-lions). From these two families, on the 
other hand, only Anoplura are recorded. 

The family FelidsB is represented by three species, the 
domestic cat, tte California lynx and the tiger. The cat 
and lynx have a common Mallophagan parasite, Tricho- 
dectes subrostratus (and no other), while the tiger has a 
biting louse presumably peculiar to it. The description 
of this parasite is, however, very brief and unsatisfactory. 

The family Viverridae, mongooses, ichneumons and 
genets, is represented in the host-list by eight species, of 
which five are of the genus Herpestes. Two of these 
Herpestes species, one of southern Spain, north Africa 
and Asia Minor, the other of west, east and south Africa, 
harbor a common Mallophagan parasite. A record of 
the finding of Trichodectes subrostratus, the familiar 
biting louse of the cat, on Herpestes pluto, comes from 
the Kameroons (Africa). It is probably a case o© 
straggling, the mongooses being common enough in gar- 
dens, and some of them fairly domesticated. 

Of the family Canidae there are records from eleven 



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268 THE AMEBIC AN NATURALIST [Vol. XLVin 

species, including the domestic dog, a wild dog of South 
America, two wild dogs of Asia, two foxes, and a wolf. 
The domestic dog has a familiar sucking louse and is also 
credited with that problematical normal or straggling 
biting louse of a peculiar genus which I have referred to 
in my account of the parasites of the kangaroos Tricho- 
dectes latus, the common biting louse of the domestic dog, 
is also conmion to the wolf, Canis lupus, of Europe and 
Asia, and to the raccoon-like wild dog, Nyctereutes pro- 
cyonoides, of Asia and Japan. The record of this last 
came, it must be noted, from the Berlin Zoological Gar- 
dens. There is no other record of commonness of para- 
site to two hosts in the family. The English fox has a 
single Mallophagan species, and the California fox has 
another. The dhole, a wild dog of the Himalayas, has a 
Mallophagan species, and the Magellan wolf of Patagonia 
has another. 

The family Procyonidae is represented in the host-list 
by two raccoons, the California ring-tailed cat, and two 
coatis of Central and South America, respectively. The 
two raccoons, Procyon lotor of North America and Pro- 
cyon psora of California, harbor a common Mallophagan 
parasite. In addition a German record (from a zoolog- 
ical garden?) credits Procyon lotor with carrying also a 
Mallophagan which is the characteristic parasite of the 
badger. On the California ring-tailed cat, Bassariscus 
astuta, have been found two Mallophagan species, one of 
which is the characteristic parasite of the skunks of 
North and South America. The two coatis, Nasua narica 
and Nasua rufa, one of southwestern United States, 
Mexico and Central America, and the other of South 
America from the equator south, both harbor a common 
Mallophagan species. 

The family Mustelidae, comprising the badgers, wea- 
sels, martens, and skunks, an ill-smelling crew, offers no 
attraction to blood-sucking parasites, but is represented 
in the host-list by nearly twenty species from which 
Mallophaga have been taken. The Old World badger has 



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No. 569] ECTOPARASITES OF MAMMALS 269 

a characteristic species, Trichodectes crassus. The mar- 
tens, weasels and ermine have also a characteristic spe- 
cies, Trichodectes retusus, which is recorded from the 
pine marten of Europe and northern Asia, the beech 
marten of the same range, still another Old World mar- 
ten, the weasel of Europe and Asia, the ermine of north 
Europe, Asia and America, and the weasel and mink of 
North America, in all six or seven species of Mustela and 
Putorius of very wide geographic range. The skunks of 
North and South America have also a characteristic 
Mallophagan species, Trichodectes nephitidis, described 
by Osbom from the conunon North American skunk. 
Mephitis mephitica, taken in Nebraska. I have found 
this parasite on the western skunk, M. occidentalis, in 
California, and on M. macrura of Arizona. It has also 
been recorded from the spotted skunk, Spilogale inter- 
rupta, of the southern United States, Mexico and Central 
America, and I have examples from a *' skunk *' of Bolivia. 
It is also recorded from a Chilian Mustelid, Galictis 
quiqui, which ranges over South America from the Eiver 
Plate south, and from another species of Galictis in 
Brazil. Finally, examples of this ubiquitous pest are 
recorded from Helictis everetti from North Borneo I The 
last record comes from Neumann, a very careful and 
weU-inf ormed student of the parasites, but his specimens 
were taken from a skin in the Museum of Natural History 
of Paris. The Old World otter, Lutra Intra, has a Tri- 
chodectes of its own, as has also an African otter, L. 
matschiei, and the North African Zorilla lyhica. 
Mjoberg records a species of Boopia (typical kangaroo 
parasite genus) from Lutra pruneri of India. As the 
record is an extraordinary one, being the only case of a 
Boopia found outside of Australia or on a mammal other 
than a Marsupial, it is well to note the exact circum- 
stances of the record. The parasites (several examples) 
were got by Mjoberg from the Hamburg Zoological Mu- 
seum where they were ticketed as having been taken 
from a ^'soeben frisch angekommenes Thier" of the 
species Lutra pruneri, the animal having been received 



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270 THE AMERICAN NATURALIST [Vol. XLVHI 

from India. There are to be considered in connection 
with this extraordinary record, first, the possibility of an 
exchange of labels in the course of the several handlings 
of the Mallophagan specimens, and, second, the possibility 
of a favorable answer to the question: Is Lutra pruneri, 
which does not appear in Trouessart at all, only Lutra 
lutra, the common Old World otter, and was the speci- 
men from which the Mallophagan came a resident in a 
zoological garden in which kangaroos or wallabies also 
lived, affording a bare chance of straggling? The similar 
aberrant records from dogs of the kangaroo parasite 
Heterodoxus have already been referred to. 

The bears (family Ursidae) have, so far, but one para- 
site record to present, a Mallophagan species, Tricho- 
dectes pinguis, having been described from the Thibetan 
bear, Ursus thibetanus, a century ago. 

The walrus (family TrichechidaB) harbors a strange 
Anopluran parasite of species, genus and family peculiar 
to its host, as, indeed, might be expected of any ecto- 
parasite daring enough to brave comrade life with wal- 
ruses. Examples of the parasite have been taken from 
walruses from Spitzbergen, Frobisher Bay (Davis 
Straits), the Hamburg Zoological Garden, and I have 
recently had them from a ** Pacific walrus'' from ** south- 
east of Siberia." 

The family Phocidae is represented in the host-list by 
at least five species of seals and sea-lions carrying an 
equal number of Anopluran species representing three 
different genera, all of them peculiar to the seals. A 
single parasite species, Echinopthirius phocce has been 
repeatedly taken from the fur seal, Proca vitulina, from 
both Old World and New World shores. The harp seal 
of the Arctic is credited with the same parasite, as well 
as another. Hooker's seal of New Zealand and the Auck- 
land Islands carries an Anopluran, Antarctopthirius 
macrochir, of species and genus peculiar to it, while the 
elephant seal of the south Pacific has another parasite 
also of genus and species peculiar to it. 

The large order Rodentia is well represented in the 



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No. 569] ECTOPARASITES OF MAMMALS 271 

host-list, representatives of thirteen families, summing 
about sixty species, being listed. Both Mallophaga and 
Anoplura infest the rodents, but certain families are 
parasitized almost or quite exclusively by Anoplura, 
while Mallophaga are the only parasites of others. 

The SciuridsB (squirrels and spermophiles), for ex- 
ample, with a dozen host species, are parasitized by a 
dozen species of Anoplura with only a single Mallo- 
phagan record; and a single record under such circum- 
stances is always suspect. There is little commonness of 
parasite species to two or more host species in this 
family. Osbom's Polyplax montana is recorded from 
the eastern and western North American gray squirrels, 
and his P. suturalis has been taken from two Spermo- 
phile species, both, however, of the same general range. 
The well-differentiated parasite genus Acanthopinus is 
represented by one species from the common Old World 
squirrel, Sciurus vulgaris, and another from the eastern 
gray squirrel of North America. These species, though 
close together, really seem to be different. In addition I 
have just found the Acanthopinus species of the eastern 
gray squirrel on Douglas's squirrel in California, and 
another (new) species on a California chipmunk. The 
only Mallophagan species recorded from a Sciurid is 
Gyropus turbinatus from the marmot, Arctomys mar- 
motta, of the mountains of southern Europe. 

From the beaver (family Castoridae) a characteristic 
Mallophagan species, Trichodectes castoris, has been 
taken in America. The beaver, it may be noted, is the 
host of the only beetle (Platypsylla cast oris) that has 
become a specialized permanent ectoparasite, passing its 
whole life on the body of its host. 

The Old World dormouse (family Gliridae or Myoxidse) 
harbors a sucking louse, Polyplax pleurophcea. 

The large family Muridae, including the rats, mice, 
voles and lemmings, is represented by twenty host species 
well scattered over the world. There are twenty-two 
Anopluran species and two Mallophagan species in the 
parasite list for the group. Both of these Mallophagan 



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272 THE AMERICAN NATURALIST [VoL.XLVm 

records are my own. One is a new species of Colpoce- 
phalum (exclusively a bird-infesting genus) from a 
''spotted rat,'* Uganda, Africa, sent me by Sjoestedt in 
a collection made by the Swedish Zoological Expedition 
to Kilimandjaro-Meru, Africa, in 1905-1906. It is un- 
doubtedly a straggler from some bird taken at the same 
time. The other is a poor specimen of Trichodectes from 
Mus rattus, Canal Zone, Panama, sent me by Dr. Jen- 
nings. It may be a good record — or it may be a deceiving 
one. Both record and specimen need further scrutiny. 
It is, perhaps, important to note that two specimens of 
a wingless Psocid (Atropidae) were sent with the lot 
labeled ** parasites from Mus rattus." It would be very 
interesting if we could know that these Atropids were 
really living on the rats, feeding on their hair or dermal 
scales. I have found Atropids in rats' nests and birds' 
nests living undoubtedly on the loose hairs, feathers and 
dermal exuviae. It is my belief, based primarily on cer- 
tain striking facts of morphology, that the Mallophaga 
are degenerate descendants of the Rsocidae.^ Of the 
murid Anoplura, two or three are common to several 
hosts, as the well-known Polyplax spinulosa, recorded 
from all over the world from the now cosmopolitan Mus 
rattus and Mus decumanus, as well as from Mus syl- 
vaticus of Europe and north Asia, and Mus alexandrinus 
of south Europe and Asia Minor (perhaps only a variety 
of Mus rattus) y and Polyplax affinis (perhaps only a 
variety of P. spinulosa) recorded from Mus agrarius of 
eastern Europe, and Mus sylvaticus of Europe and north 
Asia. Polyplax (Hoplopleura) acanthopus, the common 
sucking louse of the mouse has been taken from the now 
cosmopolitan Mus musculus, and also from Lemmus tor- 
quatus, the lenuning of Arctic Europe, Asia and America, 
Microtus agrestis, the field vole of Europe, Microtus arvor 
lis, another common vole of Europe and Asia, and Micro- 
tus sp. from Iowa, U. S. A. The water rat, Hydromys 
chry so g aster, of Australia, has a Polyplax species of its 
own as has also Otomys bisulcatus of south and central 

3 See Psyche, Vol. 9, 339, pp. 1902. 



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No. 569] ECTOPARASITES OF MAMMALS 273 

Africa, Hesperomys leucopus of North America, Epimys 
aurifer of the Malay Peninsula, Gerbellus indicus of 
northern India and Afghanistan, and Holochilus sciureus 
of Brazil and Peru. The conunon Old World mouse, Mus 
minutus, harbors three Anopluran species, while Mus 
musculus has but two. The Old World water vole. Micro- 
tus terrestris, has a parasite differing from the two in- 
festing respectively the two Old World land species of 
Microtus. 

In connection with this resume of the Murid parasites, 
I may say that I have now in process of working over 
some two hundred vials of material collected last summer 
from California mammals, which is going to add many 
records to the Murid list of both hosts and parasites. It 
will also add numerous records for the squirrels and 
spermophiles (Sciuridae). 

The family Geomyidae, gophers, is represented in the 
host list by three North American and one Central Amer- 
ican species. The Mallophagan species Trichodectes 
geomydis occurs on all of these hosts. The North Amer- 
ican hosts are Qeomys bursarius (Iowa), Thomomys 
hott(e (California), Thomomys bulbivorous (California), 
and the one Central American host is Macrotomys hetero- 
dus (Costa Rica). T. bulbivorous may be a synonym of 
T. bottcB. In addition, Qeomys bursarius has yielded an 
Anopluran species of genus and species peculiar to it. 

The pocket rats, family Heteromyidae, are represented 
by a species of Perognathus (Baja California), and 
Dipodomys merriami (Arizona). From both are re- 
corded the same Mallophagan species, Trichodectes 
californicus. 

The jerboa, Dipus sp., is the sole representative of the 
family DipodidaB. From it is recorded an Anopluran 
species taken in Tunis. 

The OctodontidaB are represented by three species 
parasitized by one Anopluran and three different Mallo- 
phaga. The three hosts are of three different genera, one 
with an African range, the other two of South America. 
The parasite species on each is peculiar to it. A third 



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274 THE AMEBIC AN NATURALIST [Vol. XLVIH 

record, crediting the characteristic Trichodectes pilosus 
of the horse to a coypou of South America (in the menag- 
erie of the Jardin des Plantes in Paris), is certainly 
either a false record or one of rather extraordinary 
straggling. The two Mallophagan species from these 
South American tuco-tucos belong to the genus Gyropus, 
which is the Mallophagan genus especially characteristic 
of the related South American families, the Caviidae 
(guinea-pigs), the Dasyproctidae (agoutis), and the Chin- 
chillidae (chinchillas and vizcachas) (see following 
paragraphs). 

The guinea-pigs and mocos (family Caviidae) are repre- 
sented by three species, and are strongly parasitized by 
Mallophaga. They have no Anoplura. The domesticated 
form, which is variously held to be a species distinct 
from any wild one now known, or a variety of the wild 
species, Cavia cutleri, harbors two well-known species of 
Gyropus, namely G. ovalis and G. gracilis (this latter is 
held by some students to be of distinct genus). In addi- 
tion, Piaget has described a species of Menopon (bird- 
infesting genus) from it, and Paine and I have described 
another Menopon from it from collections we have had 
from Peru and Panama. We have also found this latter 
species on the wild guinea-pig, Cavia cutleri, from Peru, 
and from this host Paine has described a species of 
Gyropus peculiar to this host. From the Brazilian moco, 
Kerodon moco, has been recorded a variety of Gyropus 
gracilis, one of the familiar species of the domestic 
guinea pig, as well as another species of Gyropus peculiar 
to the moco. Recently Cummings has described a new 
Mallophagan taken at Villa Rica, Paraguay, from the 
wild guinea-pig, Cavia aperea. For this new species he 
established a new genus called Trimenopon. As a matter 
of fact the species is so much like Kellogg and Paine *s 
Menopon jenningsi, except for its markedly larger size, 
that I am not at all sure it should be added as a fourth 
guinea-pig parasite. 

A single agouti, Dasyprocta aguti, from Brazil, repre- 
sents the family Dasyproctidae. From it have been de- 
scribed two species of Gyropus peculiar to it. 



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No. 569] ECTOPARASITES OF MAMMALS 275 

The chinchillas and vizcachas (family ChinchiUidfiB, 
or LagostomidsB) are represented in the host list by two 
species, to which I can add another (perhaps two others) 
on the basis of material recently received from Dr. C. H. 
T. Townsend, of Peru. From Lagidium peruanum Gay 
long ago described a peculiar Gyropns, and I have speci- 
mens of a Gyropns which may or may not be different 
from Gay's species. His description is very meager. In 
addition I am about to describe, under the name PhUan- 
dria toivnsendi, another species, representing also a new 
genus, specimens of which have been sent me by Dr. 
Townsend from the same host. Also in this Townsend 
sending are specimens of a small Polyplax species (Ano- 
pluran) from the same host. 

The CercolabidsB or CoendidaB, American porcupines, 
are represented in the host lists by five species, three of 
Central and South America and two of North America. 
They harbor no Anoplura, but are parasitized by two 
Mallophagan species, of which one, Trichodectes setosus, 
occurs on all the host species in the list. The second 
Mallophagan is a Trichodectes recently described by 
Stobbe from Cercolabes nova-hispanice of Mexico and 
Central America. The other South American host porcu- 
pines are Coendu (Cercolabes) prehensilis (northern 
South America) and C. villosus (Brazil). The North 
American hosts are Erethizon epixanthum (California) 
and E. dorsatum (Nebraska). 

Finally the family Leporidae, hares and rabbits, ap- 
pears in the host list with six (perhaps only five) repre- 
sentatives, of which four, namely, Lepus timidus, of cir- 
cumpolar arctic regions, Lepus cuniculus, native to 
Europe and north Africa but introduced over the whole 
world, Lepus europceus of Europe and Lepus campestris 
of western Canada and United States, harbor the same 
species of sucking louse, representing a genus peculiar to 
hares and rabbits. I must note that this species, Hcema- 
topinus ventricosus Denny, is commonly referred to as 
two species, of which one, H. ventricosus, is recorded 
from the American host species and L. cuniculus, while 



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276 THE AMERICAN NATURALIST [VouXLVm 

the other, called H. lyriocephalus, is recorded from L. 
timidus and L. europceus. But Neumann, an exception- 
ally experienced student of the Anoplura, holds that the 
two species are one. A deer-infesting Mallophagan, Tri- 
chodectes tibialis, certainly a straggler, has been recorded 
from Lepus europceus, and another Trichodectes (a very 
old and uncertain record) from Lepus cannabinus. 

The order Insectivora is represented by but two spe- 
cies, the mole, Scalops argentatus, of North America, 
and the shrew, Sorex araneus of Europe and Asia. Each 
harbors an Anopluran species, that of the mole being a 
curiously modified form and of species and genus peculiar 
to its host, while that of the shrew is of a species not 
found on other hosts. 

The order Prosimiae, the lemurs, presents a single 
record, that of a species of Mallophagan, Trichodectes 
mjobergi Stobbe, described from the North Bomean 
Nycticebus borneanus (family NycticebidsB). 

The order Primates is represented in the host list by 
four families, the CebidsB of the New World, the Cerco- 
pithecidae, the single family of apes, SimiidsB, of the Old 
World, and the family of man, Hominidae. The distribu- 
tion of the ectoparasites of these groups is of unusual 
interest to the special student and will likely prove equally 
so to more general students. 

The Cebidae, platyrrhine, tailed. New World monkeys, 
are represented by two species, the spider monkey and 
one of the howling monkeys of Brazil, members of differ- 
ent genera, each with a Trichodectes species peculiar to 
it. In addition three species of Ateles, one of Mexico and 
Central America, another of Guiana and Brazil, and the 
third an undetermined species of the genus represented 
by a specimen in a traveling menagerie in Europe, have 
yielded three species of the Anopluran genus Pediculus, 
otherwise characteristic of man and the anthropoid apes. 
These three Pediculus species have been recorded and de- 
scribed by three different students of the group, all careful 
workers, and there can be no doubt of the generic refer- 
ence. But it is to be noted that the specimens of all three 



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v^v 



Ko.569] ECTOPARASITES OF MAMMALS 277 

parasite species were obtained either from host skins in 
a mnsenm (in one case the Zoological Mnsenm of Ham- 
burg, in another, the Berlin Museum) or from a live host 
in a menagerie. In no case, therefore, is the possibility of 
a straggling record wholly excluded, but the coincidence 
of three discoveries makes the records practically safe. 
Finally, in this connection it is to be noted (a^ I have 
already pointed out in a brief paper*), that, although 
^i^\'\ Ateles is a tailed New World genus and presumably 

^^^^v widely separated genetically from the anthropoids, 

^. ^^ I'riedenthal has aflSrmed, on a basis of blood and hair 

comparison, that Ateles shows unmistakable diflferences 
'^e/t from other tailed monkeys, and resemblances with the 

'^ anthropoids, and he suggests that in Ateles we should see 

^^^ monkeys, which, in a certain sense, replace, in the New 

TForld, the anthropoids of the Old. It is, in any event, a 
t k strange thing that Ateles differs from the other Cebidae 

my ^nd from the CercopithecidsB as well, in not harboring the 

I'ij ^najylxiTan genus Pedecinus to which all monkey-infest- 

rifi!;. %• -Arxoplura, except those of the simians, belong, but in 

-,^ ^^^u^lly harboring parasite species of the genus found 

,, ^/sex^rlxere only on the simians and man. 

Tlx^ family CercopithecidaB, catarrhine. Old World 

^ortfer^ys, is represented in the host list by a dozen spe- 

^[^ ^^^s, f*:H*om which one Mallophagan species, viz., my Tri- 

d ^Ao^^ ^^:^tes colobi from a guereza monkey, Colohus guereza 

\\. ^^"■^- <^^::iudatus (East Africa), and ten Anopluran species 

'^^^^^ TtDeen recorded. Of the Anoplura nine species be- 

; l^^K t o the genus Pedecinus, long recognized as the char- 

^ actox-i s^tic genus of the lower monkeys, as contrasted with 

-' ^^^ S^^Tius Pediculus characteristic of the anthropoid apes 

i^ ^^^ ^^^^t^an. For the tenth species, Fahrenholz establishes 

t)^^ x^^^ genus Pthirpedecimis, just as for one of the 

^^^^^■"^^ infesting species the separate genus Phthirius had to 

^ ^^^ablished. There are several cases of the common- 

^^^ of a single Pedecinus species to two or three hosts. 

I '^^ ^'^eviceps Piaget is recorded from Macacus silenus of 

Ectoparasites of the Monkeys, Apes and Man," Science, N. S., Vol. 
^,v . ^^» Pp. 601-602, 1913. 



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278 THE AMERICAN NATURALIST [Vol. XL VIII 

India, Cercopithecus mona of west Africa, and a third 
Cercopithecus skin in the Zoological Museum at Ham- 
burg. P. longiceps Piaget is recorded from Macacus 
cyclopis of Formosa, Semnopithecus maurus var. cris- 
tatxis of Borneo, and Macacxis cynomolgus of the Malay- 
sian region. P. eurygaster Gtervais has been recorded 
from Macacus sinicus of India and on a macaque in the 
Zoological Garden at Sydney, and another in the Zoolog- 
ical Garden at Melbourne. A hamadryad (Paphio sp.) 
of north Africa has a Pedecinus species peculiar to it, as 
has a trachypithecus, of Malaysia, and the Barbary ape, 
Macacus innuus, of northern Africa and Gibraltar. The 
common Macacus rhesus carries one species of Pedecinus 
peculiar to it, and that single species of Phthirpedecinus 
already referred to. Macacus silenus also has recorded 
from it two species both belonging to Pedecinus. 

The family Simiidae, anthropoid apes, is represented 
in the host list by three species, namely, the chimpanzee 
and two gibbons. One of these gibbons is Hylohates 
syndactylus of Sumatra; the other is H. leuciscus of 
Borneo. A single species of Pediculus is common to 
them both, and is not elsewhere recorded. The chimpan- 
zee has also a single species of Pediculus which is pecul- 
iar to it. No Pedecinus has been taken from a Simian. 

Finally man, representing the fourth Primate family, 
Hominidffi, is the host of three notorious Anopluran spe- 
cies, two of which are species of Pediculus and the third 
the only species so far known of another genus, Pthirius. 
Neumann is inclined to see in Pediculus corporis only a 
variety of Pediculus capitis. All of these parasites are 
found on man in all parts of the world. Some curious 
variations among the parasite individuals are shown, 
perhaps the most curious being a plain tendency to a 
darker coloration of the individuals occurring on the 
bodies of men of the dark-skinned races. In my brief dis- 
cussion elsewhere, already referred to, I have noted the 
interesting significance of this possession by man and the 
anthropoid apes of a common genus of Anopluran para- 
sites, while the parasites of the lower monkeys belong to 



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No. 569] ECTOPARASITES OF MAMMALS 279 

a well-distinguished other genus. There is no doubt that 
the close physiological fitting of parasites to host makes 
their host distribution significant of genetic or ''blood'* 
relationship, and this commonness of one type of parasite 
to man and the apes, and its limitation to these hosts, and 
replacement on the lower monkeys by another parasitic 
type, is an added indication of the actual blood-likeness 
of the Simians and man, a likeness apparently greater 
than that between the Simians and the lower monkeys. 

Ill 

In the light of the plain statement in part I of this 
paper of my belief gained from a study of the distribu- 
tion of the bird-infesting Mallophaga, to the effect that 
the host distribution of the permanent wingless ecto- 
parasites of birds is determined more by the genetic rela- 
tionships of these hosts than by geographic relationships 
or any ecological condition, and the corollary of this, 
which is that the distribution of the parasites may there- 
fore often have a valuable significance as to the genetic 
relationships of animals whose genealogic aflSnities are 
in process of ascertainment, and in the light of the facts 
of distribution for the mammal-infesting Mallophaga and 
Anoplura as just set out in part II of this paper, I 
hardly need to do more, in conclusion, than to point out 
that the distribution conditions exhibited by the mammal 
parasites, even in the face of the meager knowledge that 
we yet have of the mammal-infesting forms, clearly, on 
the whole, confirm this thesis. In fact, considering how 
few mammal-infesting parasite species we yet know, it is 
surprising how repeatedly the commonness of parasite 
species to two or more related, although geographically 
well separated, host species, is illustrated. All through 
the order from Marsupials to Quadrumana this condition 
is again and again exemplified. I am then, naturally, 
made more certain of the essential truth of the thesis, and 
can the more strongly recommend the attention of sys- 
tematic zoologists to that practical application of it, 
which I have stated in the form of a corollary. 



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REGENERATION, VARIATION AND CORRELA- 
TION IN THYONE 

PROFESSOR JOHN W. SCOTT 
University of Wyoming 

It is well known that many Echinoderms possess a re- 
markable power of regeneration, and the results given 
here show some interesting phases of this process in 
Thy one hriareus (Leseur). The problem was suggested 
a few years ago in connection with class work in the 
Marine Biological Laboratory at Woods Hole, Massachu- 
setts. There it is a common practise for students who are 
taking the invertebrate course to keep aquaria in which are 
placed specimens brought in from various collecting trips 
in the vicinity. Students are encouraged to study the 
behavior of these animals, but their enthusiasm for col- 
lecting frequently causes them to overcrowd their aquaria, 
with disastrous results. After collecting Thyone, espe- 
cially if they are kept in stagnant water, the student is 
frequently amazed to find one or more of his specimens 
that have undergone evisceration. In this process the 
animal not only loses the principal feeding organs, the 
tentacles, and the entire digestive system, consisting of 
the esophagus, stomach and intestine ; but it also throws 
out a whole series of organs surrounding the esophagus 
including the circlet of calcareous plates, the nerve ring 
forming the central nervous system, the portion of the 
water-vascular system known as the ring canal with its 
attached stone canal and Polian vesicles, and the muscles 
which serve as retractors for the set of organs surround- 
ing and attached to the esophagus. We shall refer to 
these muscles as retractors of the esophagus. 

The remainder of the animal after evisceration con- 
sists, principally, of the dermo-muscular integument, the 

280 



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No. 569] REGENERATION 281 

cloaca with its attached respiratory trees, the single 
gonad, the radial canals of the water- vascular system and 
the major portion of the dorsal mesentery by which the 
intestine was suspended. Since this part of the animal 
continues to give reactions, the student invariably raises 
the question, ''Can Thyone regenerate the lost parts t*' 
This question was the starting point of the following in- 
vestigation. The work had not proceeded far when it 
was discovered that important individual differences 
occurred, and the question became, ''To what extent, or 
how completely, may these individual variations be re- 
produced in the process of regeneration f Curiously 
enough, the most important differences between individual 
Thyone involve structures which help to form the radial 
symmetry of the animal. Consequently the problem has 
a bearing on the phylogeny as well as the ontogeny of 
Thyone. 

In general, the results show that regeneration of all lost 
organs may occur and that there is a decided tendency to 
even reproduce individual variations. It was found that 
the Polian vesicles varied greatly in number, size and 
location. The retractor muscles in a single radius were 
single or multiple, and for each individual this variation 
was closely correlated with a corresponding variation in 
the number of Polian vesicles. Whether one or more 
Polian vesicles are present, there is a strong tendency for 
these to occur on the left side of the animal, a fact which 
undoubtedly has a phylogenetic significance. A more 
complete statement and a discussion of these results will 
be given in the following pages. 

General Structure of Thyone 
Thyone is functionally a bilateral animal. It has ante- 
rior and posterior ends, dorsal and ventral surfaces, and 
consequently right and left sides. The external opening 
of the genital duct is located near the anterior end in the 
mid-dorsal region. The structure and arrangement of 
the tentacles is alike on both sides of the animal. Even 



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282 THE AMERICAN NATURALIST [Vol. XL VIII 

the feeding reactions, as Pearse has pointed out, indicate 
a bilateral type. The single genital gland is median in 
position ; the genital duct and the stone canal are in the 
median dorsal mesentery ; a part of the intestine and the 
stomach are supported by the same structure. The respi- 
ratory apparatus is also a bilateral structure, one branch 
arising from each side of the cloaca. 



Fig. 1. Fio. 2. 

Fig. 1. A Diagrammatic Drawing from a Dissection Made by Taking a 
Longitudinal Cut in the Body Wall a Little to the Left of the Mid-vbn- 
TRAL Line. Shows the arrangement of the chief organs concerned in eylsceration 
and subsequent regeneration. B, w., body wall ; cl., cloaca ; c. p,, calcareous 
plates ; i., intestine ; {. m., longitudinal muscles ; p., Polian vesicles ; r., ring 
canal ; r. m., retractor muscles ; r. t., base of respiratory tree ; $,, stomach ; t., 
tentacles ; m. d,, mid-dorsal ; I. d., left dorsal ; {. v., left ventral ; r. d,, right 
dorsal, and r. v., right ventral, interradial spaces. 

Fig. 2. A Diagram to Show the Relation of Radial to Bilateral Sym- 
metry. The esophagus (e) is shown in cross-section, cut Just anterior to the 
stomach, and the view looks toward the anterior end. M., madreporite; r. r., 
ring canal. Other letters as in Fig. 1. 

Notwithstanding this general tendency toward bilateral 
synametry, the most conspicuous differences between indi- 
viduals involve structures of the radial type. Fig. 1 is a 
diagrammatic drawing of a dissection to show the general 



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No. 569] BEGENERATION 283 

arrangement of some of the more important structures 
studied in this experiment. The dissection was made by 
making a longitudinal cut in the body wall a little to the 
left of the mid-ventral line, and then pulling the flaps 
apart and pinning the animal down on its dorsal surface. 
The Polian vesicle is shown attached to the ring canal in 
the position where it is usually found when only one is 
present, that is in the left dorsal interradial space. It 
will be noticed that the retractor muscles are simply 
branches of the longitudinal muscles, and hence are radial 
in position. At the time of evisceration the body wall 
breaks a short distance posterior to the tentacles, the re- 
tractor muscles separate at the point where they join the 
longitudinal muscles and the intestine breaks off just in 
front of the cloaca. 

A better understanding of the radial type of structure 
will be gained by a reference to Fig. 2. This figure is a 
diagram to show the relation of the radial to the bilateral 
symmetry. The dorsal side of the animal is represented 
toward the top of the page, the esophagus appears in 
cross-section, cut just anterior to the stomach, and there- 
fore one is looking forward to the other organs shown. 
The retractor muscles, showing the position of the radii, 
are much contracted and thickened, a condition in which 
they are usually found after evisceration. The stone 
canal ending in the small madreporite is located in the 
mid-dorsal interradial space. Passing around in a clock- 
wise direction, the other interradial spaces are designated 
as right dorsal, right ventral, left ventral and left dorsal. 
Polian vesicles may be found in any of the interradii ex- 
cept the mid-dorsal space which always bears the stone 
canal. Although only one Polian vesicle is represented in 
this figure, the mid-ventral retractor muscle is shown 
double, a split condition which is characteristic when two 
or more Polian vesicles are present. This description 
will be sufficient to show the general relation between the 
radial and the bilateral sjnnmetry. 



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284 THE AMEBIC AN NATURALIST [Vol. XLVIII 

EVISCBBATION 

Only one method of producing evisceration was used. 
By placing a number of Thyone in a small aquarium of 
stagnant sea water, the supply of oxygen is soon ex- 
hausted. The animals become greatly distended, they 
crawl up on the sides of the aquarium when possible, and 
extend the siphon toward and frequently above the sur- 
face of the water. All of their behavior, including the 
pumping of the siphon, indicates that respiration is in- 
adequate. In the course of a day or two the water be- 
comes very foul ; soon some of the Thyone will eviscerate, 
and a considerable percentage will do so as conditions 
grow more unfavorable. Many, however, resist the un- 
favorable surroundings and will not eviscerate though 
kept for several days in foul water. But if the aquarium 
is now placed where it will have a continuous stream of 
water and air bubbles passing through it, the behavior of 
the animals is somewhat different. They then tend to 
contract to a minimal size, and sometimes assume a 
volume not more than one fifth to one seventh of their 
maximum distention. The respiratory movements are 
practically discontinued; the animal seeks a position as 
close as possible to the side and bottom of the aquarium. 
Contraction does not always take place immediately. To 
my surprise, after several hours I found Thyone which 
had resisted the previous unfavorable conditions now dis- 
charging their viscera. After remaining two or three 
days in the running water, and the animals had appar- 
ently become adjusted to this condition, I again set the 
aquarium to one side partly filled with water. Then, by 
repeating the conditions of the first experiment, as the 
water became foul several more of the holothurians ap- 
parently found life too strenuous to further retain their 
internal organs. When the remainder of this lot of 
Thyone was returned to running water, and again to 
stagnant water, a few additional individuals underwent 
self-mutilation. Out of a total of sixty-one specimens 
used in this lot forty of them eviscerated. That is, autot- 



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No. 569] REGENERATION 285 

omy occurred in at least sixty-five per cent, of Thyone, 
under the conditions described. Probably one reason why 
this process did not occur in a still larger number is that 
some animals occupied more favorable positions in the 
aquarium. A discussion of the cause of evisceration will 
be given later. 

When evisceration occurs it is sometimes hard to see 
just how the process takes place. Pearse ( '09) ascribes 
the process to a '* structural accident''; that is, it is due 
to a powerful contraction of the circular muscles at a time 
when the calcareous ring is well forward. **But if the 
tentacles are extended," he says, *'and the calcareous 
ring is pushed forward a break may occur at &" (a point 
in his Fig. 2 where the body wall joins the calcareous 
ring) ''as a result of the strong contraction of the circu- 
lar muscles at that point, and the visceral organs are 
forced out. . . . Whether this autotomy takes place or 
not depends upon the breaking of the inner branch of the 
longitudinal muscle bands, whose normal function is to 
retract the calcareous ring. When the strain brought 
about by the contraction of the circular muscles becomes 
too great these inner bands are torn asunder, usually at 
the point a?'' (inner end of the retractors of the calcareous 
ring). While it is true that muscular contraction and 
consequent pressure undoubtedly plays a prominent part 
in the process, close observation has convinced me that 
this is not the only factor causing evisceration. Upon 
several occasions I have watched carefully the breaking 
of the body wall near its attachment to the calcareous 
ring, and while there are times when the pressure appears 
to be strong, especially when the animal is being irritated 
mechanically, there are other times when the skin appears 
to ''melt away" or separate with very little or no pres- 
sure present. Indeed, after the skin once breaks at one 
side and the viscera escape through the opening, the pres- 
sure is relieved. But one may observe that the skin con- 
tinues to break until the calcareous ring is entirely sepa- 
rated. This, of course, would not happen if the process 



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286 THE AMERICAN NATURALIST [Vol. XL VILE 

depended entirely upon an accidental stmctural defect. 
Another thing noticed is of interest in this connection. 
When splitting open the body wall of an animal that was 
eviscerating, and thus relieving any internal pressure that 
might be due to contraction of the circular muscles, some 
of the retractors were seen still attached to the longitu- 
dinal muscles. Under these conditions it would not be 
possible for the retractors to exert any pull against the 
pressure produced by the circular muscles, yet the re- 
tractors were observed to constrict off or break away 
from the longitudinal muscles by what appeared to be 
purely a local disturbance. It is hard to see how this 
could happen, or how the skin continues to separate 
around the calcareous ring after the first break is made, 
if the process of evisceration depends solely upon the 
breaking of retractors and internal pressure. Indeed, 
the view that local changes take place in the tissues is 
supported by other facts. Leptosynapta, if left in stag- 
nant water or under other favorable conditions, under- 
goes repeated autotomous fission as the result of local 
constrictions, and Pearse states that autotomy depends 
upon the presence of the anterior portion of the body, 
and presumably upon the presence of the cireumoral 
nerve ring. However, he found in Thyone that highly 
irritating substances like acetic acid and clove oil did not 
produce ejection of the viscera. 

Nor were drugs like codene and atropine, which cause violent peri- 
staltic waves of contraction to pass over the body, any more potent in in- 
ducing autotomy. The same may be said of sodium chloride, atropine 
and clove oil, although the injection of any of these substances was 
often followed by a waving of the oral tentacles to perform feeding 
movements, thus bringing about favorable anatomical relations for au- 
totomy. 

These results would indicate that the nervous system 
is not primarily involved. Certainly the ejection of vis- 
cera may occur in Thyone without any visible external 
stimulus. 

The parts eviscerated in Thyone have already been 



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No. 569] REGENERATION 287 

mentioned. However, sometimes evisceration is incom- 
plete, as the following examples will show. On the morn- 
ing of August 4, a Thyone, which we shall later speak of 
as individual H, was found eviscerating in an over- 
crowded aquarium jar. While the process usually re- 
quires only a few seconds, or at most a few minutes, 
the intestine in this case was not completely thrown out 
until two or three hours later. This animal lived until 
killed at the end of twenty-one days. In the afternoon 
of the same day on which individual H eviscerated, an- 
other Thyone was found with the process only partially 
complete. Five hours later the intestine was still re- 
tained, and scissors were used to cut it off at its anterior 
end near the stomach. Though this Thyone received 
equally good care it died at the end of two days without 
further evisceration. A third specimen was found in- 
completely eviscerated on the above date, but it was 
allowed to stand until the next morning ; at this time the 
injured end was open, the intestine was still within the 
body cavity and a part of one of the branchial trees was 
protruding. The intestine was pulled out and broken 
oflF, after which the branchial tree was retracted and the 
injured end partially closed. This animal also died at 
the end of two days. A fourth Thyone was seized and 
by squeezing was forcibly caused to throw off the usual 
parts except the following: a part of the stomach, most 
of the intestines, and some of the retractor muscles 
which had broken off near their esophageal end. The 
next morning it had expelled the remainder of the 
stomach and intestine, two complete retractor muscles, 
and some debris which had escaped from the intestine 
into the body cavity. The anterior end of the part re- 
maining appeared ragged and imperfectly closed. It 
died on the third day. It is probable that the two re- 
tractor muscles last expelled were broken off at their 
posterior ends by local constriction, not when the body 
was under pressure. A fifth animal, which we shall 
designate as individual M, was found partly eviscerated 



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288 THE AMEBIC AN NATURALIST [V0L.XLVIII 

late on the afternoon of August 6. The next day it still 
retained the stomach and intestine and at noon the diges- 
tive tube was clipped off with scissors in the region of 
the esophagus. Nothing peculiar was noted in its behavior 
until four days later, August 11, when it discharged the 
remainder of the digestive tube. It lived and was killed 
at the end of eighteen days. These results are typical. 
The animal dies unless it is itself able to eliminate all 
organs concerned in the process of evisceration, and 
therefore regeneration does not occur unless all these 
organs are eliminated. 

The eviscerated animals show comparatively a low 
degree of mortality. In an attempt to raise twenty-five 
mutilated Thyone seven died; three of these were un- 
able to complete the process of evisceration as described 
above, and two more, since they lived for fourteen days, 
probably owe their death to other causes. The sixth 
specimen to die lived three days and had been slow in 
eviscerating. The seventh did not receive the best of 
care and died after three days. So considering the 
amount of injury the mortality is extremely small where 
proper care is taken and -evisceration is complete. 

It will not be inopportune to describe the subsequent 
behavior of the different parts after evisceration. The 
parts expelled lie on the bottom in a more or less inactive 
condition untit they die, which happens usually in the 
course of a few hours. At first the tentacles frequently 
expand and contract. They are highly sensitive, as one 
would expect, and if touched withdraw quickly into the 
esophagus and at the same time the retractor muscles 
will undergo strong contraction. By supporting these 
parts near the surface of the water, so as to insure plenty 
of oxygen, an attempt was made to keep them alive. In 
some cases the parts remained alive for two or three 
days, so this experiment appeared to be partially success- 
ful. Death is probably due to the direct exposure of 
tissues to the sea water and to the attacks of minute 
organisms. The dermo-muscular portion of Thyone is 



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No. 569] REGENERATION 289 

much less sensitive than the expelled portion, just after 
.evisceration. This is due to lack of a central nervous 
system. 

Behavior During Regeneration 
After evisceration each specimen was placed in a sepa- 
rate jar of fresh sea water. The injured end of the body 
turns in and closes up tightly, and the entire body is 
somewhat smaller than before evisceration. Respira- 
tion is slower and not so vigorous. If the water is stag- 
nant, within a few hours the animal usually climbs up 
on the side of the aquarium by means of its tube feet. 
This part of the animal therefore is capable of respond- 
ing to a lack of oxygen, and the reaction is independent 
of the central nervous system. 

The observations upon the following individual, re- 
ferred to in my notes as Thy one A, will serve to illus- 
trate the general behavior during regeneration: 

July 14, A.M. — ^Animal eviscerated itself in the usual way. In the 
afternoon it climbed up on the side of the jar and clung there evidently 
for the purpose of respiration. 

July 15-16. — Acts as on the afternoon of the fourteenth. Keeps 
closed and well contracted at the injured end. Entire body somewhat 
smaller than before evisceration, due in part to organs lost. Respira- 
tion slower and not so vigorous as normal. 

July 17. — ^In the afternoon, after water was changed, Thyone took 
up position on the sand against the side of the jar farthest away from 
the source of light. 

July 18. — The next morning it was half buried in the sand in same 
position, with a few pieces of debris pulled over it. Remained so all 
day. 

July 23. — For some two days it has been slowly burrowing down until 
only the two protruding ends of the body can be seen. When a piece 
of debris that was being held over a part of the anterior end was 
touched, this end retracted below the surface and the posterior end 
withdrew until it could scarcely be seen. Later the posterior end re- 
tracted when the shadow of my hand passed over it, the hand being held 
about one foot away. The uninjured animal is even more sensitive to 
shadow. The respiratory movements are growing stronger. 

July 28. — For the past two or three days the Thyone has been slowly 
moving through the sand in a posterior direction without uncovering 
itself. 



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290 THE AMEBIC AN NATURALIST [VOL.XLVIU 

August 2. — It is now oriented with respect to the direction of the 
light and has reached probably the darkest portion of the jar. 

August 7. — Has advanced still farther. Came about half way out of 
the sand to do this. 

August 8. — ^Reacts quickly to shadows by withdrawing, and to jar- 
ring the table. Evidently is recovering its normal behavior. 

August 10. — Has again come up about half way out of the sand. 
Reacts quickly to shadows as before. 

August 11. — Came entirely out of the sand. Spent the day on the 
sand or on the side of the jar. Appeared restless. 

August 12, 4 P.M. — Has been clinging to the side of the jar and mov- 
ing about more or less all day. Respiratory movements are strong and 
apparently normal. Has just now expanded the anterior end suffi- 
ciently for me to see the new growth of tissue formed around a penta- 
gonal opening. Fifteen minutes later it was observed to extend a set of 
minute tentacles and go through feeding movements. The tentacles ap- 
peared to be slightly more than three eighths of an inch in length. Its 
behavior continued apparently normal until it was killed twelve days 
later. 

The actions of other Thyone were studied under the 
same conditions, and we shall now give a general sum- 
mary of their behavior during regeneration. The earli- 
est reactions after evisceration take the form of contrac- 
tions resulting in the closure of the wound, and move- 
ments in response to lack of oxygen. If the oxygen 
supply is suflScient Thyone will draw itself closely into 
the angle between the side and bottom of the aquarium, 
or if the supply is deficient, it clings close to the side of 
the jar near the surface. In from three to seven days 
an instinct to burrow usually asserts itself. There is a 
tendency for the body to contract very noticeably at this 
time, and the whole organism becomes rather inactive. 
This condition is probably necessary for the formation 
of new tissue. Pearse makes the statement that in bur- 
rowing the normal Thyone will cover itself in from two 
to four hours. My observations on the mutilated ani- 
mals indicate that they require from twelve to twenty- 
four hours, in one case forty-eight hours, to complete the 
reaction. The process frequently stops for some hours 
and occasionally is never completed. In the Thyone de- 



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No. 569] HEGENERATION 291 

scribed above the animal did not begin to orient itself 
with respect to the source of light until about the twelfth 
day, but in another case the response took place on the 
second day, which shows that this reaction does not de- 
pend upon the central nervous system. It should be 
stated that normal Thyone similarly placed were used as 
controls. Thyone A was quite sensitive to shadows and 
to touch on the ninth day, but it reacted more quickly on 
the twenty-fourth day both to shadows and to mechanical 
disturbances. Whether this was due to the regeneration 
of a new central nervous system, or to a more highly 
developed specialization of function in the old tissue, I 
am unable to say. It is quite possible that both factors 
were involved. Respiration is undoubtedly correlated 
with the activity of the animal, and feeding movements 
do not occur until the regeneration of all organs is well 
established, at about twenty-seven or twenty eight days. 
The internal changes that take place during regenera- 
tion were studied in animals that were killed at different 
stages in the process. Thyone N was killed nine days 
after self mutilation. At the injured end there was a 
very small plug of tissue representing the newly formed 
esophagus; a thread-like continuation of this tissue, the 
beginning of a new stomach-intestine, was also seen in 
the mesentery. The calcareous ring and the ring canal 
were not clearly defined. Another Thyone was killed at 
about the same age after evisceration ; India ink was in- 
jected into the cloaca and into the opening at the ante- 
rior end in an attempt to demonstrate a cavity in the 
newly formed thread-like, stomach-intestine. The re- 
sults were negative and the esophagus was found to be 
tightly closed. However, the interesting observation wa^ 
made that the anterior end of each of the longitudinal 
muscles had split off a very slender branch to form a 
new retractor muscle (see Fig. 3). These newly formed 
retractor muscles were not more than one fourth inch in 
length; their anterior ends were attached in a normal 
position around the esophagus, but their posterior ends 



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292 



THE AMEBIC AN NATURALIST [Vol. XLVIII 



were attached only a short way back, much in front of 
the position of attachment of the full-sized retractors. 
In another animal killed when a day or so older, the same 
conditions held with reference to esophagus, stomach 
and intestine. At least three of the radial canals belong- 
ing to the water vascular system had branched and con- 
nected at their anterior ends in such a manner as to 
form a part of a new ring canal (cf. Fig. 4). I was un- 
able to find the rest of the ring-canal and perhaps it was 
not yet complete. 




X /-v 



FiQ. 3. Fig. 4. 

FiQ. 3. Diagrammatic Drawing to Show that in Regeneration the Rr- 
TRACTOR Muscles (r. w.) Arise by Splitting off from the Longitudinal 
Muscles {U m.). Dissected a little to the right of the mld-yentral line; d., dor- 
sal mesentery suspending the intestine {i. ) ; in,, integument ; e., region of 
esophagus. 

Fig. 4. To Show the Development of the Pentagonal Canal in a Thyone 
about Nine or Ten Days after Evisceration, r., radial canal ; p., pentagonal 
canal. The anterior ends of the radial canals fork dichotomously, and these 
branches anastomose to form the canal which later assumes a circular shape 
around the esophagus. 

Thyone F, which was killed twelve days after eviscera- 
tion, showed minute calcareous plates which formed a 
very small esophageal ring not more than one millimeter 
in diameter. The esophagus continued posteriorly in the 
form of a small tube, the stomach-intestine, which was 
suspended in the dorsal mesentery. This new digestive 
tube was about 0.5 millimeter in diameter and contained 
small, colored, movable particles that could be seen with 
the unaided eye. The ring canal was completely formed. 

Another specimen, Thyone 0, died at the end of four- 



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No. 569] REGENERATION 293 

teen days and was in bad condition when examined. The 
stomach had begun to expand and retractor muscles were 
present. Probably owing to the condition of the speci- 
men, no calcareous ring, ring canal; or Polian vesicle 
could be found. Another individual killed at about fif- 
teen days showed the stomach slightly enlarged, and the 
intestine, retractor muscles, calcareous ring, tentacular 
canals, and ring canal well formed. Two small Polian 
vescicles each about one millimeter in length were pres- 
ent. The position of the new intestine was described in 
my notes as follows : 

From the stomach the intestine follows the ventral edge of the dorsal 
mesentery, lying ventral to th'e gonaduct. At the gonad it turned ven- 
trally with the mesentery and then forward for about one half inch to 
the left interradial space; here it turns rather abruptly backward, con- 
tinuing in the mesentery below the left branchial tree to the anterior 
ventral part of the cloaca. 

At a little later stage in another specimen the intestine 
passed from the left ventral interradial to the right ven- 
tral interradial space ; then posteriorly and again to the 
left, following the ventral radial mesentery to the ante- 
rior ventral side of the cloaca. 

We see from the preceding description that all impor- 
tant organs have been reproduced in form though not in 
size, before the end of the fifteenth day. The first madre- 
porite with its tiny stone canal was found some eighteen 
days after mutilation. Twenty-one days after eviscera- 
tion in one specimen the calcareous ring was about three 
millimeters in diameter and the ampuUae at the bases of 
the tentacles were well developed. Within a week after 
this time the regenerating animal begins active feeding. 
Thy one A, killed at 41 days, was practically a normal 
animal both in behavior and appearance, except for the 
fact that the regenerated organs had not yet reached full 
size. The stomach was about one third normal size, but 
the Polian vescicles were better developed. The intes- 
tine contained a small amount of food material and was 
nine or ten inches in length; most of this growth had 



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294 



THE AMEBIC AN NATURALIST [Vol. XL VIII 



taken place posterior to the gonad. It was held in posi- 
tion as previously described and had several additional 
coils. 

Individual Variations 
To all outward appearances any two Thyone are as 
much alike as two peas. It was not until the internal 
organs were studied that important differences were ob- 






FlO. 5. DiAQBAHS TO SHOW VABIATION IN POSITION AND SiZB OP THE POLIAN 

Vesicles. P. v., Polian vesicles ; m., madreporite ; r. c, ring canal ; a-d, witb 
one Polian yesicle, e-g, with two ; h-k, with three, I., with four ; c, d., f., g., k., 
with additional rudiments of these vesicles; j., with a branched vesicle. 

served. While there are numerous minor differences, 
the most conspicuous variations are found in the num- 
ber, size and location of the Polian vesicles (cf. Fig. 5), 
and in the number and arrangement of the retractor 
muscles. On account of the radial structure of Thyone 
not more than four Polian vesicles are present, since 



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No. 569] 



REGENERATION 



295 



a homologous structure, the madreporite and its stone 
canal, occupies the dorsal interradial space. The num- 
ber of vesicles varies in fact from one to four. By a 
reference to Table I, it will be seen that out of 77 indi- 
vidually examined, 41 had one, 20 had two, 14 had three, 

TABLE I 

To Show the Number of Polian Vesicles Peesent in a Given Number 

OP Thyone. Also to Show thbib Location in the 

interradlal spaces, with reference to the 

Bilateral Symmetry of the Animal 



Number of 
PoliAD YesiolM 


Number of IndiTld- 
uala Eznmiued 


Left 
Dorsal 


Left 
Ventnil 


Right 
Ventntl 


Right 
Dorsal 


1 
2 
3 
4 


41 
20 
14 
2 
77 


38 
17 
14 
2 
71 


3 
19 
15 

2 
39 




3 

12 

2 


. 

1 
1 
2 


Totals 


17 


4 









and 2 had four Polian bodies. If one is to test the matter 
of regeneration, of course it is important to know 
whether the variations or individual peculiarities will 
be accurately reproduced. Another striking character- 
istic comes out when we note in the same table the loca- 
tion of these organs. Of the forty-one individuals which 
had a single Polian vesicle, all were on the left side of 
the animal, and 38 were in the left dorsal interradial 
space. In twenty specimens with two Polian bodies each, 
36 were on the left side and only four on the right side 
of the body. A similar asymmetrical distribution of 
these parts was found when three Polian bodies were 
present. In one specimen, however, two vescicles were 
found in one space, the left ventral interradius, the only 
instance of this kind observed; on account of this dou- 
bling, the right side lacked one of the number to which it 
was entitled in the table. Where four Polian bodies are 
present the arrangement is, of course, symmetrical on 
both sides. Still another interesting fact comes out when 
we examine the totals in the last line. Out of the 77 indi- 
viduals, 71 had a Polian vesicle in the left dorsal inter- 
radial space, 39 vesicles were found in the left ventral. 



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296 



THE AMERICAN NATURALIST [Vol. XL VIII 



17 in the right ventral, and only 4 in the right dorsal 
space. That is, the total number on the left side com- 
pared with the total number on the right side bears the 
ratio of 110 to 21. Not only is there this tendency for 
the vesicles to be more abundant on the left side of 
Thyone, but the totals show that the chances of a given 
Thyone having a Polian vesicle in any given interradial 
space decreases in a counter-clockwise direction, begin- 
ning with the left dorsal interradial position. Coincid- 
ing with the number of individuals examined, the maxi- 
mum number of chances is found in the mid-dorsal inter- 
radius, where the stone canal is always present. That is, 
the stone canal with its madreporite is a more funda- 
mental and stable structure than each or all of the 
vesicles. 

The conditions are none the less interesting when we 
compare the Polian vesicles with reference to size and 
location, as will be seen from the examination of Table 
II. The Polian vesicles are here divided arbitrarily 
into three groups, designated as large, medium and 
small, and their respective locations are shown. In addi- 

TABLE II 
To Show the Polian Vesicles with Reference to Size and Location 



Sice 


Left Donal 


Left Ventral 


Right Ventral 


Right Donal 


ToUl 


Large 

Medium 

Small 

Rudiment . . . 


56 

17 



2 


17 

22 



1 




5 

10 

5 



1 
3 

7 


73 
45 
13 
15 


Total 


75 


40 


20 


11 


146 



tion some Thyone had the rudiments of other vescicles, 
each too small to be considered a distinct pouch. These 
are designated in the table as a *^ rudiment." It will be 
noticed that all of the large, and most of the medium- 
sized vesicles are on the left side; that all the small 
ones, and most of the rudimentary ones are on the right 
side. The table as a whole shows that not only does the 
number of Polian vesicles diminish in a counter-clockwise 



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No. 569] REGENERATION 297 

direction, but their size diminishes following the same 
law. These facts appear significant and without doubt 
are suggestive of ancestral history. 

If it is true that the radial symmetry of Echinoderma 
is to be ascribed to a fixed stage in their ancestral his- 
tory, we are led to suppose that the point of attachment 
was on the right side of an originally bilateral animal. 
The life history of Pentacrinus, the larval organ of Aste- 
roidea, and a great many anatomical and embryological 
facts support this view. While it is not within the prov- 
ince of this paper to discuss the relative significance of 
these matters, the evidence is so overwhelming that the 
theory is generally accepted. It is also no doubt true 
that some groups of Echinoderms took to a free-living 
existence early in their ancestral history, and others re- 
mained fixed until comparatively a late period. As proof 
we may cite the embryological evidence that Holothurians 
develop without any attached stage whatever, that the 
Asteroids develop a larval organ and pass through a 
Sessile stage for a brief period in their development, 
while the crinoids usually remain permanently fixed 
throughout life. At least we can best account on this 
theory for the deep-seated and fundamental radial sym- 
metry of some forms; the longer the attachment the 
more deep-seated would become the type of radial sym- 
metry. Now if this theory is correct we can use it to ex- 
plain the conditions described above for Thyone. The 
ancestors of this form must have broken away from the 
fixed stage very early, for we find the radial symmetry 
not well established on the right side of the animal as 
evidenced by both the position and size of the Polian 
vesicles. Out of 118 large and medium-sized Polian 
vesicles, 112 were on the left side, while in a total of 28 
small or rudimentary Polian bodies, 25 were found on 
the right side. The arrangement of these organs in 
Thyone adds one more bit of evidence to support the 
following statement of Lankester. 



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298 



THE AMERICAN NATURALIST [VoL.XLVin 



It therefore appears that the Holothurian stock branched off from 
the Pehuatozoa before complete pentamerous symmetry of the hydro- 
coele and associated organs had arisen, before any definite calcynal sys- 
tem had developed, while the gonads were still a simple strand opening 
to the exterior by a single posterior gonopore. 

The muscles used as retractors of the oesophagus were 
other organs in which there was considerable individual 
variation. As a general rule each of the five retractor 
muscles consists of a single band that takes its origin from 
the longitudinal radial muscle about one third the way back 
from the anterior end of the body and is inserted in front 
into the wall of the esophageal ring. Such a retractor, 
however, is frequently split up into several strands vary- 
ing from two to five in number. A reference to Table III 

TABLE III 

To Show the Correlation between the Number op Polian Vesicles 

AND THE Tendency poe the Retractoe Muscles to Divide 



Number of Poli«n Vesicles 



I 



Retractor muscles, single 

Retractor muscles, multiple 

Average number retractor muscles, per individual 

Average number retractor muscles, per radius 



39 
1 

5.153 
1.030 



2 
17 
10.263 

2.052 





16 I 2 
12.400 10-000 

2.480| 2.000 



shows that in 76 individuals examined, 41 had retractor 
muscles all in single bands, while 35 specimens had these 
muscles subdivided or multiple in character. This vari- 
ation is especially interesting when considered with 
reference to the number of Polian vesicles. For in forty 
cases where one Polian body was present thirty-nine bore 
the unsplit or single retractor and there was only one 
specimen with these muscles showing a multiple number. 
In thirty-six cases where two or more Polian vesicles 
were present, all but two had the retractor muscles in a 
split or divided condition. If we consider each strand 
as a separate retractor muscle, we may then obtain the 
average number of retractors per individual for any 
definite number of Polian vesicles. By a reference to 
the fourth horizontal line of Table III, one finds that the 
average number in individuals with one Polian vesicle is 



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No. 569] REGENERATION 299 

just slightly in excess of five, the pentameric number, 
and the average number when two Polian vesicles are 
present is 10.263. This ratio is only partly maintained 
when three vesicles are present, for the average number 
is then 12.400, and in the two cases with four vesicles the 
average was just twice the pentameric number. It is 
therefore evident from the facts shown in this table that 
with an increase in the number of Polian vesicles there 
is associated a strong tendency for the retractor muscles 
to take on a split character. If it were not for the fact 
that the split character shows considerable variation in 
the same individual one might suggest that the tendency 
to divide is correlated with the greater functional activ- 
ity of the water vascular system as evidenced by the in- 
creased number of Polian vesicles and the location of the 
longitudinal muscles that lie along and just internal to 
the radial canals. About all one can say is that corre- 
lated with a more complete radial symmetry with respect 
to the Polian vesicles, there is a greater plasticity in the 
retractor muscles, causing them to divide longitudinally 
into separate muscle bands. 

To what extent, or how completely, may these indi- 
vidual variations be reproduced in the process of regenera- 
tion! An answer was obtained in the following way. 
First a close examination was made of all parts eviscer- 
ated and a record was kept of all organs showing variable 
structures. Special attention was given to Polian vesicles 
and to retracter muscles. The mutilated specimens were 
then placed in separate aquaria in which the water was 
changed frequently to prevent it from becoming stale. 
After a considerable interval these animals were killed 
and the regenerated organs were compared with the lost 
parts. Table IV shows several individuals compared in 
this way. The number of retractor muscles found in each 
radius is given in the order of the radii taken in a clock- 
wise direction. A study of the table indicates that there 
is a strong tetndency to reproduce individual peculiarities, 
as shown by individuals B, E, G, H, M and 0. This does 



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300 



THE AMERICAN NATURALIST [VoL.XLVHI 



not always hold true, for individual L reverted toward 
the more radial type of symmetry. From these few cases 
it would appear that individual peculiarities tend to pre- 
dominate over ancestral influences in the process of re- 

TABLE IV 

To Illustrate the Relation between Beoeneration and Original Sym- 
metry IN Thyone 



IndiTiduAl 


OrlglDAl Sjmmetrj 


Regenerated Symmetry 


Used 


PoliAD Vetfcles 


Retractor Muadea 


Pollan Vesicles 


Retractor Musclfs 


B 
E 

H 
L 
M 

W 


2 

2 + 

2 

2 

1 

u 


2-2-2-2-2 
3-3-2-2-2 
1-1-1-1-1 
1-2-2-2-1 
1-1-1-1-1 
1-1-1-1-1 
2-2-2-2-2 


2 

2 

2 

2 + 

2 

? 

? 

2 

2 

2 


3-3-2-3-3 
2-3-2-2-2 
2-1-1-1-1 
2-2-2-2-2 
2-3-2-2-2 
1-2-1-1-2 
2-2-1-2-2 
2-2-2-3-4 


X 






2-2-2-2-2 


Y 




2-2-1-2-2 



generation. Specimens W, X, Y, are included in this 
table to show further the correlation between Polian ves- 
icles and retractor muscles. 

Discussion and Summaby 
There remains to be discussed the general bearing of 
the foregoing experiments. First, the difference in the 
number of Polian vesicles in different Thyone is partly 
compensated by a variation in size, the fewer the number 
the larger their size, though this ratio would, not be an 
exact one. In other words the total volume of the Polian 
vesicles in any given specimen bears a general relation to 
the size and functional activity of the animal. Notwith- 
standing this functional relationship since the actual 
number varies so widely it would be interesting to com- 
pare the number found in other species of holothuria with 
the conditions in Thyone. The data secured on this ques- 
tion were meager and not very definite. For example, 
Packard in one of the older text-books says in speaking 
of Thyone, 



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No. 569] REGENERATION 301 

There are three Polian vesicles, one fusiform and an inch in length, 
the two others slenderer. 

Clark ('02) gives the number for Thyone briareus 
(Leseur) as usually one or two; for T. scahra (Verrill) 
as usually single, and for T. unisemita (Stimpson) as 
one. He also mentions six other holothurians found in 
the Woods Hole region and all have a single Polian ves- 
icle except Cucumaria frondosa (Gunnerus), which usu- 
ally has one. He says nothing of the position in which 
these vesicles are found. In another paper ( '01) Clark 
mentions a large holothurian about 40-45 centimeters in 
length {Holothuria mexicana Ludwig) in which there is 
a great diversity in the number of tentacles and Polian 
vesicles. The tentacles vary from 18 to 21, while the 
Polian vesicles vary from 1 to 9. The number of speci- 
mens examined, sixteen, was hardly suflBcient to obtain an 
adequate comparison ; two had 1 vesicle each, two had 2, 
five had 3, three had 7, one had 8, and one had 9. It is 
probable that if one were to examine a large number of 
individuals of each species, with reference to the number 
and location of the vesicles, he would obtain further inter- 
esting results. Lang ( '96) cites a number of groups of 
holothurians in which only one vesicle has been observed ; 
but states that there are a number of species in other 
groups that have occasionally or usually more than one. 

Where accessory vesicles occur they vary greatly in number, and ap- 
pear to have very slight, if any, systematic significance. Where only one 
Polian vesicle occurs it lies in the left ventral inten-adius, very seldom 
in the left dorsal interradius. Where two or more vesicles occur, they 
are also mostly formed in the ventral region of the circular canal. 

Since Lang describes Cucumaria as the type specimen, 
in which the Polian vesicle is said to be in the left ventral 
region, it is possible that his generalizations were based 
principally on this form. At any rate, the conditions in 
Thyone seem to give a more definite significance to the 
number and location of thB Polian vesicles. 

Various explanations of autotomy and evisceration have 
ieen suggested, many of them having a teleological char- 
acter. The view that the holothurian offers up the better 



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302 THE AMERICAN NATURALIST [VoL.XLVm 

part of itself to appease the hunger of its enemy lacks 
confirmation, since the viscera are distasteful to fishes 
and to some other animals. It may be that the autotom- 
ous elimination of the Cuvierian organs serves a defen- 
sive purpose, as pointed out by Ludwig and Minchin, and 
Minchin suggests that the viscera may also be lost in this 
process and thus incidentally be associated with a pro- 
tective response. In the case of Thyone, however, evis- 
ceration can hardly be considered defensive, and certainly 
it is not a process of self -division for only one part pro- 
duces a new individual. Clark ( '99) in discussing self- 
mutilation in the synaptas states the matter clearly in 
the following terms : 

I agree entirely with Cuenot ('91) in believing that autotomy is not 
normal or defensive but is due entirely to pathological conditions. I 
never saw a case of it in synaptas supplied with plenty of sand and an 
abundance of sea water. 

Lang ( '96) points out one of these pathological condi- 
tions, and recounts the fact that 

A Stichopus was observed to come entirely out of its skin, t. e.j the 
whole integument dissolved into slime, so that only the dermo-muscular 
tube enclosing the viscera remained. 

In the present paper I have mentioned that Thyone at 
times appears to undergo a similar softening of the 
tissues in the region where the break occurs, and Pearse 
('09) showed that autotomy is due, at least in part, to a 
structural arrangement which he considers is accidental 
in character. My observations further show that local 
constrictions undoubtedly have an important part in sepa- 
rating the retractors from the radial longitudinal muscles. 
All of these factors are pathological and are due to exter- 
nal or internal stimuli. The external (extra-cellular) 
stimuli, mechanical and chemical, as tried by Pearse 
('08), appear to be less effective in producing autotomy 
than the purely internal (intracellular) stimuli such as 
lack of oxygen and its associated phenomena. The chem- 
ical (strychnine) that produced the largest percentage 
of evisceration in Pearse 's experiments, probably affected 
respiration, since it greatly increased the activity of the 



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No. 569] REGENERATION 303 

animal; therefore the need of oxygen would be propor- 
tionately greater than the supply, and the Thyone ren- 
dered more susceptible to evisceration. Now while autot- 
omy undoubtedly enables the animal to maintain its exist- 
ence for a considerable period on a smaller supply of 
oxygen, the times when this would become necessary in 
nature are probably rare, and it would be futile to specu- 
late upon what evolution yet has in store for the process. 

According to Lang, the retractor muscles of the oral 
region have been derived by the splitting up of the ori- 
ginally simple longitudinal muscles, and this specializa- 
tion became more marked as the oral tentacles became 
more highly developed and required increasing protec- 
tion. Species are to be found in the Dendrochirotae in 
which the separation and branching off of retractors from 
the longitudinal muscles has not yet been perfected. In 
regeneration the retractor muscles of Thyone are derived 
in the same way, i. e., by splitting off from the longitu- 
dinal muscles, and such progress is made that they are 
fairly well developed by the time the tentacles take up the 
function of feeding. The increasing sensitiveness and the 
later activity of the regenerating animal are presumably 
associated with the development of a new nervous system. 

If we may regard the bilateral echinoderm larva as 
representing an early phylogenetic stage rather than a 
larval adaptation to a free-swimming existence, we will 
now discuss the symmetry of Thyone. As stated above, it 
is generally agreed that the radial arrangement of parts 
of the echinoderm body is due to a fixed stage in its 
ancestral history. Some holothurians and spantangoids, 
show in their ontogeny first a free stage, second a radial 
stage, and finally a bilateral adult. During the develop- 
ment of asteroids that have a fixed embryonic stage, the 
early bilateral symmetry is soon disarranged by the 
development of organs on the left side of the animal. 
For example, the left hydrocoele takes the form of an un- 
closed water-vascular rosette which grows around the 
esophagus to form the ring canal and its appendages, and 
its connection with the dorsal pore gives rise to the stone 



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304 THE AMEBIC AN NATURALIST [Vol. XL VIII 

canal. Excepting the echinoids and erinoids in which 
there is either no distinct Polian vesicle or else a simple 
glandular structure, those echinoderms that have retained 
the most distinctive type of radial structures have also 
as a rule, retained the most symmetrical arrangement of 
the Polian vesicles. Presumably these forms, the aster- 
oids and ophiuroids, have quite recently abandoned the 
fixed stage, and each individual usually has four Polian 
vesicles and a stone canal, one in each interradius. 
Among most of the holothurians a secondary bilateral 
symmetry has become superimposed over the radial type, 
and it is reasonable to suppose that there was a time in 
the ancestral history of Thyone when the Polian vesicles 
were symmetrically and radially disposed, or else the 
animal quit its fixed habits before the radial symmetry 
of the vesicles was thoroughly established. In the one 
case we would have a regression, a sort of backward 
retracing of the steps of evolution, or, which seems more 
probable, the ancestors of Thyone began a free-living 
existence before the radial arrangement of the Polian 
vesicles had become complete. Also the fact that the 
embryology of the holothurian egg is probably much 
compressed and shows no trace of a fixed stage indicates 
that the corresponding ancestral stage was compara- 
tively short, or, very remote. Since the modem habits of 
Thyone are bilateral, and since it is altogether improb- 
able that such habits would produce the present arrange- 
ment of Polian vesicles, the position of these organs must 
be due to ancestral influence. 

Now the Polian vesicles are capable of contracting and 
expanding and their function when they are well devel- 
oped is to act as accessory reservoirs of the water-vas- 
cular fluid. Muscle and connective tissue in the wall of 
the vesicle furnish the means to do this work. Of course, 
if the ampullae are well developed there is little or no 
need of Polian vesicles, as is the case in Asterias. But, 
though the size and number of these vesicles is function- 
ally correlated with the general development of the 
water-vascular system, especially of the oral tentacles, 



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No. 569] REGENERATION 305 

and hence shows great variability in the different species 
of holothurians, this does not in any way explain the 
great excess of these vesicles on the left side of Thyone 
briareus. In regeneration, probably through the influence 
of functional correlation, there is a tendency for the old 
tissue to reproduce the exact number and arrangement 
of the lost vesicles, but it may reproduce a somewhat 
more radial (ancestral) arrangement. 

Enough has been given in this paper to show the need 
of a more extensive and intensive reexamination of the 
Polian vesicles. This would give a better idea of their 
morphological and functional significance. The follow- 
ing sunmaary and conclusions are based on the work 
described : 

1. Evisceration in Thyone includes the following or- 
gans: Esophagus, stomach, intestine, calcareous ring, 
nerve ring, tentacles, ring canal, Polian vesicles, stone 
canal with madreporite, and the retractor muscles of the 
esophagus. 

2. The method used to produce evisceration was to 
allow Thyone to stand in stagnant water imtil it became 
foul. This was followed by treatment with rimning water 
containing much oxygen. Alternating these processes 
produced as high as 65 per cent, of self -mutilated indi- 
viduals. 

3. The structural accident theory of Pearse is inade- 
quate to explain all of the conditions arising in the proc- 
ess of autotomy. At times the skin appears to dissolve 
away with little or no pressure present, and retractors 
frequently break off by local constrictions instead of by 
longitudinal pull. 

4. The parts eviscerated are at first highly irritable, 
and may be kept alive for some time. The part remain- 
ing is less responsive, but reacts to touch, to lack of 
oxygen, and probably to other stimuli. 

5. Regeneration of all lost organs may occur, but it 
takes place only when all parts concerned in evisceration 
are completely expelled. Otherwise the animal dies. 



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306 THE AMEBIC AN NATURALIST [VouXLVm 

6. During the process of regeneration the behavior 
gradually becomes more responsive and finally is like the 
normal individual. This appears to be correlated with 
the growth of a new nervous system. 

7. Thyone is functionally a bilateral animal, but the 
most conspicuous individual differences involve struc- 
tures that have a radial arrangement. 

8. The Polian vesicles vary greatly in number, size 
and location. There is a strong tendency for these to 
occur on the left side, and this arrangement is undoubt- 
edly due to ancestral conditions, for the present bilateral 
habits of Thyone could probably have no influence in 
producing this asymmetry. 

9. The retractor muscles in a single radius consist of 
single or multiple strands, and this variation is closely 
correlated with a similar variation in the number of 
Polian vesicles. No explanation is forthcoming for this 
peculiar plasticity of the retractor muscles, but the sug- 
gestion is made that it may be functionally correlated 
with the development of the water- vascular system. 

10. It was found from the study of a number of speci- 
mens that individual peculiarities of structure tend to be 
reproduced in the process of regeneration. In this proc- 
ess it would appear that individual variations tend to 
predominate over generalized ancestral influence. 

11. Autotomy enables Thyone to survive for a consid- 
erable period on a smaller than normal supply of oxygen. 
Nevertheless, the conditions which give rise to self -muti- 
lation are seemingly in all cases pathological. 

12. The conditions in Thyone afford some evidence for 
believing that when this animal abandoned the fixed stage 
the Polian vesicles conformed more or less to the radial 
type. This is opposed to the statement of Lang that in 
all cases where a multiple number is now present ** there 
was originally only one vesicle.'' It is believed that the 
present arrangement of Polian vesicles in Thyone can be 
best accounted for on the theory of phylogenetic influ- 
ence. That, in general, those vesicles have retained their 
most complete radial arrangement in those species of 



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No. 569] REGENERATION 307 

echinoderms which have maintained to a high degree 
the functional activity of the water-vascular system. 

References 
Bather, F. A., and Goodrich, E. S. 

'00. A Treatise on Zoology. Ed. by E. Ray Lankester. Pt. 3. The 
Echinodermata. London, 
aark, A. H. 

^09. The Affinities of the Echinoidea. Am. Nat., Vol. XLIII, pp. 
682-686. 
aark, H. L. 

'99. The Synaptas of the New England Coast. Bull. U. S. Fish Com., 

1899, pp. 21-31. 
'00. The Echinoderms of Porto Rico. Bull. U. S. Fish Com., 1900, 

pp. 231-263. 
'02. The Echinoderms of the Woods Hole Region. Bull. U. S. Fish 
Cbm., 1902. 
Cuenot. 

'91. Etudes morphologiques sur les Echinodermes. Archiv, de Biol, 
Vol. XI. 
Gerould, J. H. 

'96. Anatomy and Histology of Caudina arenata, Proc, Boston Soc. 
Nat. Hi8t., Vol. 27, pp. 8-74. 
Grave, C. 

'03. On the Occurrence among Echinoderms of Larvae with Cilia ar- 
ranged in Transverse Rings, with a Suggestion as to their Sig- 
nificance. Biol. BiUl, Vol. V, pp. 169-186. 
'05. The Tentacle Reflex in a Holothurian, Cucumaria pulcherima, 
Johns Hopkins Univ. Circ, Vol. 24, pp. 504-^07. 
Henri, V. 

'03. Etudes des contractions rhythmiques des vaisseauz et du poumon 
aqueaux chez les Holothuries. C. B. Soc, Biol., Paris, T. 55, pp. 
1314-1316. 
Johnson, R. H., and Hall, R. W. 

'00. Variations and Regeneration and Synapta inhcerens. Science, 
N. S., 1900, p. 178. 
Lang, A. 

'96. Text-book of Comparative Anatomy. London, Vol. II. 
Ludwig, H. 

'96. Echinodermen. Bronn's Klassen u. Ord. des Tierreichs. Bd. II, 
Abt. 3, Buch 1. 
Morgan, T. H. 

'01. Regeneration. The Macmillan Co., 1901. 
Packard, A. D. 

'81. Zoology for High Schools and Colleges, 1881. 
Pearse, A. S. 

'08. Observations on the Behavior of Thyone hriareus (Leseur). Biol. 

Bull, Vol. XV, pp. 259-286. 
'09. Autotomy in Holothurians. Biol. Bull, Vol. XVIII, pp. 42-49. 



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SHORTER ARTICLES AND DISCUSSION 

TERMS RELATING TO GENERIC TYPES 

In the field of biological taxonomy an important reform is in 
progress. The change is from the method of concepts to the 
method of types, in order that names may be applied with 
greater precision and permanence. Under the method of types 
we no longer think of the technical name of a plant or an animal 
as attaching primarily to a concept embodied in a description or 
definition, but as relating to the first representative of the group 
that became known to science. In determining the application 
of a specific name we go back to the original specimen or type 
on which the description was based. The original description 
has become secondary to the original specimen. In like manner 
generic names are treated as relating primarily to groups of 
species, with the original species as the generic type.^ 

Without waiting to appreciate the fundamental nature of the 
change from concepts to types, many systematic workers took it 
for granted that generic types were to be determined by elimina- 
tion, in much the same way that generic concepts had been 
treated, by gradual subdivision, restriction and removal of com- 
ponent groups. The general results of elimination were the 
same as under the method of concepts: The applications of 
many of the older generic names did not become definitely fixed, 
but remained dependent upon varying individual opinions of 
the validity of the work of later authors. It often happened 
that after elimination was accomplished only the doubtful or 
unidentifiable species remained to serve as generic types. Grad- 
ually it became apparent that the practise of elimination was 
inconsistent with the method of types, and could not insure 
stability in the application of names. Recourse was then had, 
especially by zoologists, to the arbitrary designation of generic 

1 Cook, O. R, 1898, "The Method of Types," Science, N. 8., 8: 513; also 
1900, "the Method of Types in Botanical Nomenclature," Science, N. 8., 
12: 475, and 1902, "Types and Synonyms,'' Science, N. S., 15: 646. 
Swingle, Walter T., 1913, "Types of Species in Botanical Taxonomy," 
Science, N. S., 37 : 864. 

308 



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No. 569] SHORTER ARTICLES AND DISCUSSION 309 

types, the apparent object being to preserve the results of elimi- 
nation, even though the theory had to be abandoned. Probably 
it is only a question of time until the results of elimination will 
be discarded, as well as the theory, and replaced by the actual, 
historical types. 

A plan for determining the historical types of genera was 
adopted in 1907 in the American Code of Botanical Nomencla- 
ture, and other applications of the method of types are being 
rocognized by zoologists. Specialists in many groups are en- 
gaged in the study of generic types, and the need of a special , 
terminology to facilitate work of this kind is becoming appar- 
ent. Thus in Bulletin 83 of the U. S. National Museum, **Type 
Species of the Genera of Ichneumon Flies,'' by Henry L. Vie- 
reck, two new terms, **isogenotypic" and ** monobasic," are em- 
ployed in treating of the application of generic names to type 
species. The paper is of interest, not only to students of this 
group of insects, but also as an example of the tasks that con- 
front all taxonomists who appreciate the need of basing their 
work upon types. The distinctions to which the special terms 
refer are undoubtedly useful, and the possibilities of express- 
ing them in more convenient form are worthy of consideration. 

The word **isogenotypic,'' is used with reference to cases 
where two or more generic names have been applied to the same 
type species.^ For this purpose a new term is not needed unless 
zoologists are unwilling to borrow from botanical nomenclature 
a more convenient method of treating the same class of eases. 
The botanical code provides a classification of synonyms, and 
applies the word **typonym" to a name that has to be rejected 
because an earlier valid name was proposed for the same type. 
The formation and use of typonym are in accord with a familiar 
analogy. As a preoccupied name becomes a homonym, it is easy 
to remember that the use of a preoccupied type results in a 

2 A diflferent combination might have been expected, such as * * autogeno- 
tjrpic'^ or * * deuterogenotypic, " since isogenotypic suggests the notion 
of equally good types or of equal numbers of types, instead of con- 
veying the idea of one and the same type, or of a second use of the same 
type. Genera have been termed * * isotypical * ' when they were described 
from more than one species, but all truly congeneric, on the assumption that 
such species would have equal standing as types. A still older use of the 
word **i9otype'' had reference to equal representation of a genus by similar 
or corresponding species in different geographical regions or geologic periods. 
See Schuchert, Charles, 1905, U. S. National Museum Bulletin 53, Ft. 1 : 16. 



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310 THE AMERICAN NATURALIST [Vol. XLVIH 

typonym. A name based on a different type species, but eon- 
generic with the type of an older genus, is termed a metonym. 
A name rejected for lack of an identified type is a hyponym, 
and one rejected for linguistic reasons, a caconym. All rejected 
names fall readily into these five classes. 

The other new term, *' monobasic," is used by Mr. Viereck to 
indicate genera with only one species at the original place of 
publication. In botanical literature the word ''monotypic" is 
often employed in this sense, though also applied to genera that 
consist of only one species. If previous use disqualifies mono- 
typic, the same objection lies against monobasic. In addition to 
an older chemical meaning, the same word was employed several 
years ago in a biological sense, to describe a condition of descent 
in simple lines.* Apart from being preoccupied, the word mono- 
basic has a misleading implication, since under the method of 
types each generic name is referred to a single type species. 
The idea of a genus being based on many types is discarded 
with the method of concepts. Appreciation of this incongruity 
may explain why no such term as "symbasic" or *'polybasic'* 
is used in contrast with monobasic, to indicate genera that were 
first proposed in connection with more than one species. 

Evidently there is need of a simple and consistent terminology 
for indicating relations between generic names and type species. 
The normal relation under the method of types is the designa- 
tion of the type species at the original place of publication of 
the genus. Genera provided with types by original designation 
may be described as orthotypic, or normal-typed. With ortho- 
typic genera there is no occasion to raise the question of how 
many species were included at the original place of publication. 

8 Cook, O. F., and Swingle, W. T., 1905, ** Evolution of Cellular Struc- 
tures," Bull. 81, Bureau of Plant Industry, U. S. Department of Agricul- 
ture, p. 20. Plants or animals with specialized habits of asexual reproduc- 
tion, such as vegetative propagation, parthenogenesis or self-fertilization, 
would be described as monobasic. The second edition of the Standard Dic- 
tionary defines monobasis as follows: "The derivation of a stock from a 
single parentage by inbreeding, or by propagation of buds or cuttings; 
opposed to symbasis." Thus the danger of ambiguity in using monobasis 
for nomenclatorial purposes is greater than in using monotypic, though it 
must be admitted that the use of the word monotypic in two senses may 
sometimes result in confusion. Genera that were monotypic in the strictly 
nomenclatorial sense of being established in connection with one species may 
not be monotypic in the more general taxonomic sense of including only one 
species. 



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No. 569] SHORTER ARTICLES AND DISCUSSION 311 

Genera that are not orthotypic fall into the two classes al- 
ready considered, those with a single species at the original place 
of publication, and those with two or more species. It is now 
generally agreed that when only one species was mentioned this 
should be accepted as the type. Such genera may be called 
haplotypic, or single-typed. When two or more species were in- 
cluded in the original treatment of a genus, and no type was 
designated, we have the problem of subsequent determination of 
the type, resulting in what may be termed a logotypic genus, 
that is, a genus with a rationally selected type species. The 
object of selection is to determine the historical type of the 
genus. Names must have definite applications, and historical 
applications of generic names can be made definite by ascertain- 
ing the historical types. The recognition of a new generic group 
is usually based on one leading or dominant species, with the 
others added as associate members. 

In many cases the generic type is intimated by the original 
author in dividing the genus into subgenera or sections, in illus- 
trating one of the species or citing illustrations published in 
earlier works, in naming the genus with particular reference to 
one of the species, in recording economic uses, or in giving geo- 
graphical or other indications of greater familiarity with one of 
the species. If the application of these or other historical cri- 
teria leaves more than one species eligible for selection, the first 
of the eligible species should be taken as logotype. In this way 
it is possible to develop a consistent system of type selection that 
will commend itself as reasonable and give the same results in 
the hands of different students.* 

4 Simply taking the first species under a generic name as the type would 
probably establish more of the generic names in their historical places than 
the method of elimination, which accepts the last of the original species left 
in the genus as the type. Either of these methods of selecting types would 
result in many cases of separation of generic names from their historical 
types, but these undesirable changes in the application of names can be 
avoided by taking the historical considerations more directly into account, 
as in the American Code of Botanical Nomenclature. Probably a more sat- 
isfactory system for associating generic names with their historical types 
could be developed by sufficient study of the problem. A policy of refusing 
to revive generic names that were not directly associated with binomial spe- 
cies to serve as types, would avoid many of the changes threatened by un- 
mitigated priority. In proposing lists of **nomina utique conservanda" in 
advance of any provision for the definite application of names, European 
botanists have demonstrated one more way to put the cart before the horse. 



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312 THE AMERICAN NATURALIST [Vol. XLVHl 

In addition to the three ways of associating generic names 
with their type species, there are many cases where generic 
names have been applied to groups that do not include the type, 
or any of the original species. Formal assignments of errone- 
ous types also occur when generic names are not traced back to 
their original places of publication, or when ineligible species 
are designated as types. In dealing with the synonymy of 
genera previously treated under names that belong to other 
groups it will be convenient to have a distinctive term for this 
class of cases. Such misplaced names, applied to groups that do 
not contain the true type, may be indicated as pseudotypic, or 
false-typed.^ 

It should be expected that more critical analysis of taxonomic 
problems would lead to more definite distinctions and more pre- 
cise terms. The older terminology was developed to facilitate 
the study of names, whereas it is now apparent that provision 
must be made for the study of types as another formal branch 
of biological taxonomy. Nomenclature has a history of three 
hundred years while systematic typology is only beginning. To 
gain further insight into these typological problems is obviously 
more important than to attempt premature applications of par- 
tial solutions. It may take fifty or a hundred years to transfer 

Failure to regulate the application of names is the fundamental defect of the 
Paris and Vienna codes, and is hardly to be cured without thorough re- 
casting. 

5 Thus the palm genus Martinezia, as treated by Kunth, Martius, and 
many later writers as relating to Martinezia caryotwfolia and its immediate 
relatives, was pseudotypic, for this species does not appear to be congeneric 
with any of the five species originally referred to Martinesia by Buiz and 
Pavon. Hence it has been proposed to replace this pseudotypic use of Mar- 
tinezia by a new generic name, TiXmia, (See Bull, Torrey Bot, Club, 28: 
565.) The five original species of Martinezia belong to three natural groups, 
now recognized as distinct families, the first two species to the Cocace®, the 
third species to the AcristacesB and the others to the Chamsedoreacese. The 
third species, M, ensiformis, should be taken as logotype of Martinezia be- 
cause the figures used to illustrate the generic characters evidently represent 
a member of the family Acristacese. Another reason for excluding the 
cocoid species from consideration as type is that they are mentioned as 
deviating from the ''essential characters of the genus,'' in connection with 
the original description. The rule of the Vienna code, to the effect that the 
name of a subdivided genus should go with the majority cf the species, would 
carry the name Martinezia over to the family ChamsBdoreace®. The making 
of such a rule shows that many European botan'sts were still working imder 
the method of concepts, and were not accustomed to think of generic names 
as inseparably connected with type Spec'es. 



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No. 569] SHORTER ARTICLES AND DISCUSSION 313 

the whole structure of biological taxonomy to the new founda- 
tion of types. To suppose that any permanent adivantage can 
be gained by elaborating defective methods under forms of legis- 
lative enactments or judicial decisions is to show a limited ap- 
preciation of the nature of the subject and of its historical de- 
velopment. As long as legislation and interpretation are based 
on inadequate study, they can represent, at most, only a tem-* 
porary consensus of opinion, for it is of the very nature of 
science to condemn and throw aside any doctrine or method that 
has proven inadequate or fallacious. 

Terms Relating to Synonyms 

The following classes of synonyms were recognized in 1907, 
in the American Code of Botanical Nomenclature:** 

Homonym, — A name rejected because of an earlier applica- 
tion of the same name to another genus. 

Typonym, — ^A name rejected because an older name was based 
on the same type. 

Metonym, — ^A name rejected because an older valid name was 
based on another species of the same genus. 

Hyponym. — ^A name not associated with a type.^ 

9 Bulletin of the Torrey Botanical Club, 34: 167, 1907. .-r— . 

7 Much confusion would be avoided by a consistent policy of withhold- 
ing recognition of generic names that have not been associated with type 
species. Thus the name Acoeloraphe, proposed by Wendland in 1879 in an 
analytical key to genera of fan-palms (Bot, Zeitung, 37: 147), was not as- 
sociated with a type, though evidently relating to a species mentioned in the 
same paper as *'Bmhea serrulata," This Florida palm differs from the 
Mexican type of Brahea in the leaf characters assigned to Acoeloraphe in 
the key and in the seed character indicated by the generic name, the al- 
bumen being solid instead of having a deep channel along the raphe. But 
Acoeloraphe being left without a type, another name, Serenoa, was proposed 
by Hooker f. in 18S3 for **Sabal aerrvXata R. & S.'' (Genera Plantarum, 
3: 926). All subsequent writers have accepted Hooker's name, and Acoel- 
oraphe should remain under Serenoa aa a hyponym. Nothing has tended so 
strongly to bring the principle of priority into disrepute as the incontinent 
revival of abortive names, to replace properly established names in current 
use. No species was referred to Acoeloraphe until 1907, when Beccari 
(Webbia, 2: 107) applied the name Acoeloraphe wrightii to a Cuban mem- 
ber of a genus that had been described in 1902 under the name Paurotis, 
a Bahaman species, Paurotis androsana, being the type (Mem. Torrey Bot, 
Club, 12: 21). This transfer of the name Acoeloraphae to the genus 
Paurotis was followed by Sargent in 1911 (Trees and Shrubs, 2: 117), but 
Beccari 's genus Acoeloraphe is a metonym of Paurotis, and is also pseudo- 



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314 THE AMERICAN NATURALIST [VOL.XLVni 



Terms Relating to Type Species 

Orthotype. — Type by original designation. A species desig- 
nated as type in connection with an original publication of a 
generic name. A genus whose type was formally designated at 
the original place of publication is orthotypic. 

Haplotype. — Type by single reference. A single species re- 
ferred to a genus at the original place of publication, and on 
this account accepted as the type. A genus proposed with refer- 
ence to a single species is haplotypic. 

Logotype, — Type by subsequent determination. The histori- 
cal type of a genus, selected from two or more original species. 
A genus whose type is selected from two or more original species 
is logotypic. 

Pseudotype, — Erroneous indication of type. A species erro- 
neously indicated as the type of a genus. A genus treated on 
the basis of an erroneous type, or so as to exclude the true type, 
is pseudotypic. 

0. F. Cook 
BuEEAU OF Plant Industry, 
U. S. Department or Agriculture, 
March 13, 1914 

typic, because of the original application of the name to Serenoa. Two 
species of Paurotis are supposed to exist in Florida, one that is identi- 
fied with the Cuban P. urightU (Grisebach & Wendland) and a local species, 
P. arhorescens (Sargent). 



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NOTES AND LITERATURE 

LINKAGE IN THE SILKWOEM MOTH 

One of the most striking recent developments in the study of 
genetics is the discovery of linkage in many of those forms which 
were supposedly thoroughly worked out. The most recent ex- 
ample* is a very interesting paper by Y. Tanaka,^ entitled 
** Gametic Coupling and Eepulsion in Silkworms." The data 
presented in this paper demonstrate the existence in the silk- 
worm moth of a group of four pairs of linked genes. Following 
Tanaka's nomenclature we may designate these genes as follows: 
N, which differentiates the larval color pattern known as 
** normal'' from that called ** plain"; S, occurring in larvae 
having the ''striped" pattern, and epistatic to N; M, the differ- 
entiator for the **moricaud" larval pattern, also epistatic to 
N; Y, the gene which differentiates caterpillars with yellow 
blood and yellow cocoons from the recessive whites. Of the six 
possible combinations of these genes, taken two at a time, all 
but NM and SM were made, and all showed linkage. Fj 
''coupling" tests, i. e., from matings where both dominants 
entered the cross from the same Pi individual, were made for 
SY and for MY, In each case there occurred cross-overs, or new 
combinations of the characters, in such proportions as to lead 
Tanaka to suppose the ratio of parental combinations to cross- 
overs among the gametes to be about as 7:1. "Repulsion" 
(where one dominant entered from each P^ individual) Fj 
results were obtained for NS and for NY, In neither case did 
any double recessives (cross-overs) appear, though over 3,000 
caterpillars were obtained in the case of NY, and 224 in the case 
of N8. From these data Tanaka concludes that the repulsion was 
complete in these two cases. It has, however, been pointed out by 
Morgan^ that such results will be obtained if the linkage is com- 
plete in one sex only. In Drosophila such "repulsion" crosses 
never produce double recessives in Fj, and it has been shown 
that this is due to complete linkage in the male, crossing over 
being frequent in the female between some pairs of genes. In 
order to test this possibility it is necessary to mate doubly hetero- 
zygous individuals to double recessives, when the gametic ratio 
is obtained directly and without the complications present in 
most Fg results. It so happens that Tanaka reports two such 
crosses, one for each sex, though he does not recognize their im- 

1 Jour, Coll, Agr,, Tohoku Imper. Univ., Sapporo, Japan, V, 1913. 

2 Science, N. S., XXXVI, 1912. 

315 



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316 THE AMERICAN NATURALIST [Vol. XL VIII 

portance in this connection. When a male heterozygous for S 
and for Y, one dominant having been derived from each parent 
(SysY), was mated to a doubly recessive {sysy) female, there 
were produced 63 8y and 65 sY — no cross-overs. A female 
heterozygous also for S and for Y, but having them ** coupled" 
(SYsy), was mated to a male sysy, and produced 215 SY and 
188 sy — again no cross-overs. Yet that crossing over may occur 
between these two pairs of genes is shown by the fact that the 
** coupling*' F2 results indicated a gametic ratio of about 
7:1:1:7. We are, therefore, still left in the dark as to whether 
crossing over occurs in only one sex, or in both. But it is certain 
that the strength of linkage in this case is not always the same — 
a point of great interest and importance. Similar cases have been 
reported by Baur* in Antirrhinum, by Punnett* in the sweet pea, 
and by the writer^ in Drosophila, 

Tanaka refers to his case as differing from previously reported 
cases of linkage in animals in that the sex differentiator is. not 
one of the genes involved, and in that the linkage is sometimes 
only partial. However, he refers several times to a paper by 
Morgan* in which it is clearly shown that three of the sex-linked 
genes in Drosophila also show partial linkage to each other, inde- 
pendently of their sex-linkage. Punnett,^ in referring to the 
same paper, has said, ** Morgan's experiments with Drosophila 
suggest coupling of some kind between factors for eye color and 
shape of wing, though both of these factors may show sex-limited 
inheritance in other families." A study of the data referred tOy 
or of any of the similar data on Drosophila since published, will 
show that these genes always show sex-linkage, and that at the 
same time they always show linkage to each other when both can 
be followed in the analysis. The two phenomena are not mutu- 
ally exclusive, but both are always present. 

Both Tanaka (in a footnote) and Punnett refer to the latter 's 
case in rabbits as the first example of linkage in animals not 
involving sex. If the linkage between sex-linked genes is, for 
some strange reason, not considered to belong in this category, 
there are still at least two cases which antedate Punnett 's slightly. 
A few months before Punnett 's paper appeared I had suggested* 
the possibility of linkage in mice. It now seems rather probable 
that -the relation in both mice and rabbits may really be that of 

8 Zeits, f, ind. AbsUu, Vererh.-Lehre., VI, 1912. 

^Jour, Genet., Ill, 1913. 

5 Science, N. S., XXXVII, 1913. 

ojaur, Exp. Zool, XI, 1911. 

tJour. Genet., II, 1912 (Nov.). 

8AMER. Nat., XLVI, 1912 (June). 



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No. 569] NOTES AND LITERATURE 317 

triple allelomorphism. For this reason I am inclined to assign 
priority to Morgan and Lynch,® whose paper on linkage of genes 
in Drosophila which are not sex-linked appeared after my own 
paper and before Punnett's. 
Columbia University A. H. Sturtevant 

NABOURS'S BREEDING EXPERIMENTS WITH 
GRASSHOPPERS 

In a recent paper, Nabours ('14) describes breeding experi- 
ments that he has been carrying on for some years with grouse 
locusts of the genus Paratettix, His work is of special interest 
in showing that in a wild species there exists a number of distinct 
types that show alternative inheritance of a particular kind. His 
paper may be summarized as follows : 

1. Nine distinct, true breeding forms of Paratettix were col- 
lected **in nature." These ** species" (as Nabours is inclined 
to consider them) **are mainly distinguished by their striking 
color patterns." 

2. When an individual of one of these species is mated to one 
of a different species the hybrid character of the oflEspring is 
apparent at once, in that **all the characters of each parent are 
represented in the F^ hybrid. ' * In other words, the hybrid is in 
a certain sense an intermediate, and **the terms dominant and 
recessive" are probably not ** applicable at all." This point, 
while of little theoretic importance, has a practical value in that 
the zygotic constitution of any hybrid can be recognized without 
further breeding tests. 

3. With one exception, each color pattern factor was found to 
behave as an allelomorph to any other color pattern factor. 

4. The various lengths of the wings and pronotum are appar- 
ently not inherited, as such but are determined by environmental 
factors, especially such as tend to prolong or to shorten the length 
of larval life. 

It appears that Nabours confuses the relation of the facts men- 
tioned under 3, and that he supposes this to be the ordinary 
behavior of "mendelizing characters," for he says: 

The essential result of these experiments has been the extension of 
this principle [Mendelian inheritance] to a considerable number of 
tjrpes of a phylogenetically low group of ametabolous insects. 

To be sure, he recognizes that other workers in genetics have 
an attitude quite different from his, and he takes some little pains 
to make clear his own point of view. To quote again (p. 142) : 

• Biol Bull, XXIII, 1912 (Aug.). 



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318 THE AMEBIC AN NATURALIST [Vol. XLVHI 

The existence of unit characters in the De Vriesian sense does not 
appear to have been as clearly demonstrated as that of alternative in- 
heritance . . . and the interpretations are at great variance. Thus, one 
group of authors [reference made to Bateson, Doncaster, and Tower] 
recognize characters in organisms that can be replaced by other char- 
acters when the proper crosses are made, . . . while on the other side 
there are those [references to Whitman and Montgomery] who believe 
that the organism as a whole is the only unit and that there are no 
actual unit characters. 

Again he says (p. 169) : 

No character of one parent species is ever replaced in the F^ hybrid 
by any character of the other parent. All the characters of each parent 
are represented in the F, hybrid. It follows then that these grass- 
hoppers do not exhibit characters which by crossing can be replaced by 
other different characters; the whole pattern appears to be the only 
unit. 

There is no real conflict between Whitman's idea and the 
accounts given by students of Mendelism, for the latter realize 
that far-reaching somatic effects may result from a single factor, 
and the composite character of the hybrid is not an uncommon 
occurrence. Nabours identifies a particular pattern with the 
* 'organism as a whole/' but since his evidence relates here to 
color patterns only, nothing is gained by the introduction of such 
a vague phrase as the ** organism as a whole." Specifically he 
shows that the hereditary differences between any two types can 
be explained on the assumption of a single differential for each 
case. 

With reference to the antithesis presented by Nabours, it must 
be recognized that the modern literature of Mendelian heredity 
affords innumerable instances where two or more characters 
entering from one parent and their allelomorphs from the other, 
reappear in the Fg generation in new combinations. 

If we assume with Nabours that each of the eight color patterns 
are represented by a characteristic condition of the "germinal 
material," we may use his terms A, B, C, D, E, F, H or I to 
symbolize this ** germinal material" for the various color 
patterns. As Nabours uses the terms, an individual homozygous 
for A is represented simply by A, and a hybrid between A and B 
by AB. In ordinary usage, the homozygous form would be 
represented as AA and its germ cells by A. This is a minor 
matter. Ordinary usage has the advantage of being more 
consistent. 

According to Nabours, then, A mated to B gives AB; S mated 
to F gives BF; C mated to E gives CE, etc. In gametogenesis 
these factors segregate, so that, for example, BA gives germ cells 



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No. 569] NOTES AND LITERATURE 319 

A and B; BF gives B and F, etc. In other words, he treats the 
matter as if he were dealing with a system of multiple allelo- 
morphs, though he nowhere specifically calls them such. From 
this point of view there are eight distinct allelomorphs con- 
cerned with color pattern any two of which may constitute a 
pair; in any zygote two allelomorphs (perhaps alike, perhaps 
unlike) will be present, and in any gamete only one of the eight 
will normally occur. 

With one exception of which I will treat later, all of Nabours's 
results can be explained by this hypothesis. This sort of explana- 
tion is not new. (ShuU ('11), de Meijere ('10), Sturtevant 
('13) and others have used it to explain results obtained in 
Lychnis, Papilio, rabbits and other forms, and it will almost un- 
doubtedly be shown to apply satisfactorily in still other cases. 

The exception just mentioned occurred in the cross which 
Nabours describes at the bottom of page 156 (e). Here a male 
of the constitution CE was mated to a female of the constitution 
BI, On Nabours 's theory, the gametes of the male should carry 
C or E, but not both, and the gametes of the female should carry 
B or /, but not both. The union of the two kinds of sperms with 
the two kinds of eggs should give four classes of offspring, and 
these were in fact obtained ; viz., 12 BC, 11 BE, 7 CI, 10 EL But 
there appeared also on^ individual BEL Nabours 's explanation 
of the case is that perhaps the BI * 'female parent gave at least 
one gamete containing the factors for the patterns of both her 
parents and that this double character gamete was fertilized by 
one of the E gametes which came from the CE male." * Let us 
see whether this is the most probable interpretation. 

As Sturtevant has pointed out, for any case to which the idea 
of multiple allelomorphism is applicable, an equally valid ex- 
planation may be found in ** complete linkage" of the factors 
concerned. To decide in any case between the two explanations 
would be impossible. 

If, however, linkage were not complete, a ** cross-over" class or 
''recombination" class might occur, and this would suffice to rule 
out the explanation based on multiple allelomorphs. 

Such a "cross-over" class perhaps is furnished by the BE I 
individual. The demonstration of this may be given by the use 
of symbols, as follows : 

Let us assume that A is the allelomorph of a, B that of b, C of 
c, D of d, F of /, / of i, etc., making eight pairs of allelomorphs 
altogether. Assume that each gamete of any individual carries 

1 This explanation is essentially similar to that advanced hj Bridges ( '13) 
to explain certain peculiar results in DrosophUa, Bridges assumed that in 
garnet ogenesis the two X -chromosomes of a whiteeyed female failed to segre- 
gate (in Bridge's terminology, non-disjunction occurred), and passed over 
together into one gamete. 



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320 THE AMERICAN NATURALIST [Vol. XLVin 

one allelomorph of each pair, and that the eight factors thus 
present in a gamete form a linked group, tending to segregate as 
a unit in gametogenesis. Thus Nabours's form A would give 
gametes of the form Abcdefhi, AB would give gametes of only 
two forms, one corresponding to A and the other to B, viz., 
Abcdefhi and aBcdefhi, Two other forms are possible, formed 
by the exchange of A with B, and of a with 6, but these will not 
occur if linkage is complete. In dealing with the hybrid AB in 
practise the factors cdefhi would not be put into the formulas, 
as they are alike in all gametes. 

These rules would apply similarly to all other species and 
hybrids. Therefore in the case in which the BEI individual 
occurred, we would represent the male parent, which Naboure 
designated CE, by bCei-bcEi, and its gametes by bCei and bcEi, 
The female parent, which Nabours designates BI, we would 
represent by Bcei-bcel, and its gametes would be Bcei and 
bcel if linkage were complete. If linkage were not complete there 
would occasionally be formed gametes bcei and BceL One of 
these latter (Bcei) was probably formed and fertilized by a 
sperm of the type bcEi, thus giving rise to the BEI individuaL 
No gametes corresponding to bcei appear to have been fertilized, 
though of course we do not yet know what the appearance would 
be of an individual so formed. 

This matter would be easy to test, and it is to be hoped the 
cross may be repeated. If then BEI forms should appear again 
and in these when mated to other forms the factors B and I should 
be found to stay together to the same extent as they before sepa- 
rated, it would show that close linkage, rather than multiple alle- 
lomorphism explains this particular instance. 

It may be, too, that both linkage and multiple allelomorphism 
play a part in the production of these phenomena. In any case 
it seems that the test is at hand, and not difficult to perform, 
excepting in so far as there are practical difficulties connected 
with the rearing of the grasshoppers in sufficient numbers to 
cover the point. 

Literature Cited. 

Bridges, C. B. 1913. Non-disjunction of the Sex Chromosomes of Droso- 
phila. Jour, Exp, Zool,, Vol. 15. 

de Meijere, J. C. H. 1910. Ueber Jacobsons Zttchtungsversuche bezttglich 
des Polymorphismus von Papilio Memnon L. ?, etc. Zta, ind. Ahsi.- 
Vererb.-Lehre, Vol. 3. 

Nabours, B. K. 1914. Studies of Inheritance and Evolution in Orthoptera, 
I. Jour, Genet., Vol. 3. 

ShuU, G. H. 1911. Reversible Sex Mutants in Lychnis dtoica. Bat, Gaz^ 
Vol. LII. 

Sturtevant, A. H. 1913. The Himalayan Rabbit Case with some Consid- 
erations on Multiple Allelomorphs. Am. Nat., Vol. XLVII. 
Columbia University John S. Dextbb 



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322 TEE AMERICAN NATURALIST [Vol. XLVIII 

distinct species. Arbitrary rules for species making, de- 
signed to restrict the activities of the more vigorous 
** splitters '' have been indeed laid down by experienced 
and conservative systematists. The final test, however, 
so far as any exists, is acknowledged to be whether a 
group breeds approximately true to its kind and is ap- 
proximately sterile with other closely related stock, and 
yet in how few cases have both or either of these criteria 
been actually applied by the describer of species ! 

As a matter of fact no stock that has been bred on a 
vast scale, so far as I am aware, breeds absolutely true to 
specific characters. In Morgan's Drosophila^ and De 
Vries's (Enothera, numerous mutants appear, probably 
through the absence of certain chemical elements, or by 
unusual combinations of elements, in the chromatin of the 
germ plasm. That this phenomenon has not been shown 
for many other species is due, in all probability, to lack 
of close attention to all the individuals in a huge proces- 
sion of stock in the process of breeding. Any insect bred 
as extensively as Drosophila ampelophila, the pomace fly, 
has been would probably show as many mutants; some 
would show more. C olios eury theme, the ** orange sul- 
phur '' or alfalfa butterfly, is such an example. Though 
this butterfly can not be bred on a scale comparable with 
Drosophila, every thousand individuals yield many dis- 
continuous variations : red eyes instead of green, tongue 
uncoiled instead of wound in close flat spiral when at rest, 
one antenna shorter than the other, the absence of certain 
spots from the wings, gynandromorphism, caterpillars 
with two longitudinal rows of large black dorso-lateral 
spots or white dorso-lateral stripes upon a dorsal surface 
usually unmarked, caterpillars with one proleg less upon 
one side than the other. This is a partial list of points at 
which the descendants of three females of Colias eury- 
theme failed in a single summer to breed true to the char- 
acteristics of the species, though bred under uniform 
normal conditions. The fact that these discontinuous 

1 Science, N. S., Vol. XXXIII, Nos. 847, 849, pp. 496-499, 534-537, 1911. 



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No. 570] SPECIES-BUILDING 323 

variations appear under uniform external conditions 
leads one to be very skeptical toward most of the past 
experimental work supposed to show the effects of the 
environment upon insects in modifying the germ cells. 
Any one wishing to try an experiment on the production 
of variations by the influence of the environment, or upon 
the inheritance of acquired characteristics, should deny 
himself absolutely this privilege until he shall have bred 
under normal conditions at least a thousand individuals 
of the stock that he will subsequently employ. 

That species necessarily breed true to the specific char- 
acters ascribed to them by their inventors is an unveri- 
fied dogma. At best the reporter picks out stray individ- 
uals here and there from a vast procession of which he 
can only see glimpses, and, trusting to the credulity of the 
public in the established ideas about these matters, he 
creates upon paper a new species. Doubtless the unit 
characters of ^* specific ^^ grade in the stock of some spe- 
cies are more generally constant or homozygous than 
those of certain others, but it is reasonable to suppose 
that, owing to dominance the heterozygous^ condition re- 
garding certain characters is frequently masked and un- 
noticed in apparently pure strains of wild stock. If the 
heterozygote respecting a certain character be compara- 
tively rare, or if it be a heterozygote based on several 
interacting factors, like redness in the kernel of Nilsson- 
Ehle's wheat,^ it may cross again and again with 
the homozygous dominant, or with another heterozygote 
of similar nature to itself, without the appearance in the 
population of the recessive. That specific and varietal 
characters do exist in heterozygous condition in wild 
stock of * * pure ' ' species, unmasked by dominance and 
easily detected, I have found to be the case in Colias at 
several points. The color pattern as a whole apparently 
fluctuates in variation, but these variations in detail are 

2 The mixed Mendelian condition, I>(i2), producing germ cells D and B 
in equal numbers. 

8 Act. Univers. Lund, 1909. 



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324 THE AMEBIC AN NATURALIST [VoL.XLVHI 

strictly a matter of inheritance. Its *' fluctuation ** is not 
due to a difference in environmental conditions surround- 
ing different individuals, but evidently to the condition of 
the germ plasm. The parents of any brood may be 
heterozygous or homozygous for the determiners of color 
pattern. If they come from a strain homozygous in this 
respect and are alike in appearance, the offspring will 
resemble the parents closely and show a narrow range of 
variation, but if unlike and derived each from imlike 
parents, a wide range of inherited '^fluctuation" occurs. 
Such is often the case in the inheritance of a melanic 
tendency so often attributed to the action of the environ- 
ment, and of spots used in the diagnosis of species as, for 
example, the conspicuous spot in the middle of the imder 
side of the hind wing. This is commonly double in Colias 
philodice and C. eurytheme, consisting of a chief and an 
accessory spot, single in C. palceno, an arctic circumpolar 
species, but it varies enormously. In eurytheme and 
philodice the accessory spot may be absent ; in palceno, in 
rare cases, it may be present. I have bred large families 
of C. eurytheme in which both the chief and accessory 
spots were, like those of the parents, almost uniformly 
large and nearly equal in size. In other families, from 
parents in which the accessory spot is nearly or quite 
lacking, the offspring show a similar reduction. In 
C. philodice I have found it possible by selection to estab- 
lish a race devoid of the row of submarginal red-brown 
spots of the under side of the wings. Thus, by selection, 
strains, nearly or perhaps quite homozygous for definite 
points of color pattern, may be established, derived from 
a population which in the main is in an extremely hetero- 
zygous condition. Yet species are named and distin- 
guished on the basis of these features. 

Another example of heterozygous condition of a char- 
acter within a wild species is the white pigment in the 
ground color of the '' albino " female of Colias, both in 
the yellow species, philodice and the orange species, 
eurytheme. The white female is regularly heterozygous 



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No. 570] SPECIES-BUILDING 326 

for this sex-limited character. Her daughters are white 
or colored (yellow or orange, as the case may be) in equal 
numbers. Still another interesting heterozygous feature, 
though not of *^ specific '' grade, was seen last summer in 
a pure strain of Colias eurytheme. A female appeared 
that could not upon stimulation coil up her tongue. 
Mated with a normal male, this abnormality was in- 
herited in various degrees by half her offspring (37 
uncoiled and 28 coiled). One of her daughters, abnormal 
in this respect and mated with a normal of a different 
strain, transmitted the abnormality to about 16 per cent. 
of her offspring (29:151), showing that the possessor of 
this abnormality is regularly heterozygous in respect 
to it. 

Whether (Enothera lamarckiana is or is not a complex 
hybrid produced from two American species, is it not 
certain that, like other wild and cultivated stock, it does 
possess characters for which it is heterozygous, and that 
the watcher for mutants frequently seizes upon rare com- 
binations of recessive features as a part of his elementary 
species f 

But to breed true is only a secondary criterion of spe- 
cies. Inbred strains of domestic animals and plants do 
that to a certain degree. Varieties and races to a certain 
extent may do the same. The real criterion (and the one 
least often practically used by the systematist) is fertility 
within the group and sterility with other closely related 
groups. Here dogma holds sway among writers on or- 
ganic evolution as well as among systematists, for we are 
told by those who have been accustomed since childhood 
to the idea of the objective reality of species that hybridi- 
zation of species, that is, genuine species in good and 
regular standing before the scientific public, has played 
very little part in the origin of new species. This atti- 
tude was entirely logical in view of the accepted ultimate 
definition of a species. If the individuals of one species 
are actually sterile with members of another, hybridiza- 



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326 THE AMERICAN NATURALIST [Vol. XLVIII 

tion of species can not play an important part in the manu- 
facture of new wild strains. But only in comparatively 
rare instances have attempts been made experimentally 
to mate Linnaean species. The dogma of the objective 
reality and uniform value of the species unit has diverted 
us from seriously attacking this problem. Just as in the 
nineteenth century the fixed idea of the immutability of 
species blocked the progress of the doctrine of evolution, 
so this dogma now stands in our way, and obstructs the 
possibility of vision. We need now fully to recognize the 
fact, which most biologists are ready to admit, that the 
term species is applied to most heterogeneous groups of 
individuals, groups of every conceivable size, based on 
differences that are most diverse in number and impor- 
tance, often separated from allied groups entirely by the 
arbitrary judgment of the describer, and depending ulti- 
mately upon his personal temperament. These groups, 
as already stated, have been tested in comparatively few 
instances by the only reputable criterion that can be 
applied in the separation of closely allied groups, that of 
sterility or fertility inter se. 

To one who tries to divest himself of the accepted ideas 
regarding species and is on the watch for evidence of 
hybridization among imlike strains that we are accus- 
tomed to call species, new cases of such hybridization 
frequently come to light. Especially is this true among 
the insects. In regions where the faunal areas of two 
*^ good " species overlap or are contiguous, such crossing 
not infrequently occurs. 

A most interesting case is that of the four species of 
the coccinellid beetle Adalia that occur in the same region 
in Colorado, as worked out by Palmer.* These four forms 
with clean-cut differences in color and color pattern had 
been named and described by different authors as dis- 
tinct species, yet three of them were found to be inter- 
breeding with complete fertility but still respectively 
maintaining their identity, forming a regular Mendelian 

, ^'Annals Entom. Soc. America, IV,' 3, September, 1911. 



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No. 570] SPECIES-BUILDING 327 

epistatic series : a red-brown spotless form, melanopleura, 
dominant at one end of the series, then annectans, a red- 
brown, spotted type, and finally the recessive, melanic, 
red-spotted humeralis with a color pattern different from 
that of annectans or of Coloradensis, another red-brown, 
spotted type of that locality. *' But ^^ says the upholder 
of the present idea of species, '^ here we have a single 
polymorphic species, not three or four different species. 
The breeding experiments show that the describers of 
these forms were wrong in ascribing systematic rank to 
mere color varieties.'' It goes, of course, almost without 
saying that the makers of these species did not before 
naming their beetles, breed them to determine whether 
they would breed true to type and were infertile 
inter se. Indeed, in how few cases has this been done! 
Even the larval stages of most known beetles are imper- 
fectly unknown, much less the possible genetic relation- 
ship of one type to another, as determined by breeding 
them to maturity. BlaisdelP describes the case of two 
Californian Coccinellidse which are found in winter in 
small groups under the bark of eucalyptus trees. '* Usu- 
ally there was one Olla plagiata with each of the groups 
[of 0. abdominalis], irrespective of whether they were 
made up of two or more individuals." The same author, 
by selection of specimens of abdominalis representing 
different types of color pattern, describes its range of 
variation, but adds that his studies throw no light on the 
relationship of the two species. Had he bred certain in- 
dividuals of 0. abdominalis together, it is not at all un- 
likely, in view of his observation of the regular occur- 
rence of a few plagiata in every group of abdominalis^ 
that the former interbreeds with the latter and may be a 
simple recessive in respect to it. Miss Palmer's work 
on the allied Adalia certainly suggests this as a possi- 
bility. 

Another remarkable case is that of the nine true-breed- 
ing species of grouse-locust, Paratettix, recently de- 

^Entom, News, Vol. 24, No. 9, November, 1913. 



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328 THE AMERICAN NATURALIST [Vol. XLVni 

scribed by Nabours.® These nine color types, or species, 
freely interbreed. The color pattern of the resulting Fi 
hybrid in each case is a mosaic combination of those of 
the two parents. The latter in subsequent inbreeding 
may be extracted intact, each having been transmitted as 
a distinct unit, without dominance. 

In Lepidoptera, an order in which polymorphism is 
notoriously common, hybridization between species has 
been frequently observed. Standfuss^ devotes eight 
octavo pages of his excellent *' Handbuch '' simply to the 
enumeration of examples of such hybridization between 
palaearctic species of moths and butterflies, and acknowl- 
edges that he mentions only a fragment of all such cases 
on record or preserved in collections* This list would be 
greatly extended if American species were included. 
Seven different hybrid combinations within the genus 
Colias in the palsearctic region have been noted by Stand- 
fuss. 

Colias philodice, the clouded sulphur or clover butterfly 
of the eastern and central United States, readily crosses 
with C. eurytheme, the orange sulphur or alfalfa butterfly 
of the western and central states. The territory of philo- 
dice, according to Scudder extends like a wedge westward 
from the Atlantic into the faunal area of eurytheme. 
Overlapping thus occurs in the Mississippi Valley, though 
philodice does not extend as far southward as the Gulf 
States, Texas, Louisiana and Mississippi, in which 
ei^rytheme is found. 

These two species are fairly sharply distinguished by 
the difference in the ground color, which in eurytheme is 
orange, in philodice sulphur yellow. The middle spot of 
the upper side of the hind wing is brilliant orange in 
eurytheme, pale orange or yellow in philodice. The dark 
border of the hind wing of the female is wider in eury- 
theme than in philodice and broken with a row of large 
yellow spots. 

6 Journal of Genetics, Vol. 3, No. 3, February, 1914. 

7** Handbuch d. palUarktischen Gross-Schmetterlinge/ ' 1896, p. 51-53. 



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No. 570] SPECIES-BUILDING 329 

It has long been known that these two species hybridize 
in the Mississippi Valley, where both occur. By extended 
experiments during the past summer and previous au- 
tumn with eurytheme stock sent to me from Arizona 
through the kindness of Messrs. V. L. Wildermuth and 
E. N. Wilson and with philodice from New Hampshire, I 
have found that the two species mate together readily, and 
produce vigorous offspring. The species-hybrid males 
were then mated with eurytheme females, and more than 
half of the pairs (viz., four out of seven) were fertile. 
Mated together, however, the species-hybrids showed 
much sterility. Out of ten such matings, nine were in- 
fertile. From the tenth pair, nineteen adult butterflies 
were produced. 

Orange in this cross is distinctly dominant over no 
orange, or yellow, but the color of the heterozygote is a 
pale orange overlying yellow, and is by no means as bril- 
liant as the almost fiery orange of the large, summer 
seasonal variety, the typical ** eurytheme.^* In broods 
emerging the last week in August and the first three 
weeks of September, when intense color may be expected, 
the heterozygote is pale orange, corresponding approxi- 
mately to the variety known as keewadin, whereas those 
raised in the greenhouse and emerging early in December, 
resemble the small orange-yellow winter type known asi 
ariadne. Keewaydin, according to Wright,® occurs at all 
seasons in California, though probably more abundantly 
in spring and autunm. Hence he regards this as the 
typical variety, rather than '^eurytheme/' It is inter- 
mediate, however, in size and intensity of color. 

In general, therefore, there is an incomplete dominance 
of orange, the color of the heterozygote corresponding 
either to that of the intermediate or to that of the winter, 
seasonal variety of eurytheme, depending upon the time of 
the year when, and the environmental condition under 
which, the cross is made. The wide, spotted margin of the 
hind wing in the female eurytheme, moreover, when pres- 

8'*Butterflie8 of the West Coast of the United States," p. 119. 



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330 THE AMERICAN NATURALIST [Vol. XLVIII 

ent in marked degree, is dominant over the narrower 
margin in philodice. This dominance of the orange mani- 
fests itself quite as distinctly if the albino female of 
eurytheme, instead of the orange female, is bred to the 
yellow philodice male. The daughters of such a family 
in one case (0, 1913) were 36 white, 35 orange; the sons, 
numbering 72, were, of course, all orange. The white 
species-hybrid (FJ is identical in appearance with the 
albino eurytheme, the female color pattern of the latter 
(wide marginal bands) being dominant, and the orange 
middle spot both in pure bred albino eurytheme and in 
the albino hybrid being usually paler than in their orange 
sisters. 

The second hybrid generation inbred (Fg) shows a well 
marked segregation of the sulphur-yellow color of phUo- 
dice, as a simple Mendelian recessive. Three out of the 
sixteen colored (non-albino) individuals of the brood ob- 
tained in December, 1913, are definite recessives of clear 
sulphur yellow, with pale yellow middle spots on the hind 
wing. The most highly colored individuals are four that 
correspond in hue to pale examples of the light orange- 
yellow winter variety, ariadne. There is no return, at 
least in this winter brood (enclosed in a greenhouse in 
New Hampshire in December), to the brilliant orange of 
the grandparent al eurytheme stock. Nor do they even 
return to the suffused light orange (intermediate) tint 
of the heterozygous father (keewadin type), for the 
ground color of all individuals of this brood (Fj) is 
yellow, either flushed or spotted, except in three indi- 
viduals, with orange. 

An interesting case of probable hybridization in the 
allied genus M eg ano stoma, or dog's head butterfly, is re- 
corded by Wright® between the Califomian M. eurydice 
and M. ccrsonia, common throughout the southern states. 
The two species are remarkably different in color and 
have different food plants. The male of eurydice differs 
from that of ccesonia in having a violet luster and lackmg 

9Loc, cit.f p. 116. 



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No. 570] SPECIES-BUILDING 331 

the black border upon the hind wings possessed by 
ccesonia; in the female, etirydice is clear yellow with no 
dark border, while in cccsonia the female has a wide 
border similar to that of its male, though less well marked 
on the hind wings. The probable hybrid called amorphce 
is a female, intermediate in color between the typical 
ccesonia and eurydice. That is, the border of ccesonia 
crossed with no border (if my interpretation is correct) 
is incompletely dominant. Wright says: 

At one time I was of the opinion that AmorphcB was a hybrid between 
Eurytheme and Caesonia . . . but of late years, as no male Amorphce 
is known, I have concluded that Amorphce is simply a dimorphic female 
[of eurydice]. 

Possibly it is both, an example of dimorphism produced 
either by immediate hybridization, or by a mutation re- 
sulting from some previous hybridization. That a male 
appears to be lacking in this case would not be an argu- 
ment against the possibility of hybridization, for by such 
crossing the sex ratio is frequently upset, the product 
being of one sex only. But it appears to be possible that 
the male of this cross is that described as M. bernardino, 
a variety of eurydice found in the mountains of the same 
region where amorphce also occurs. It is an interesting 
combination of the male coloration of both species, having 
the violet hue of eurydice that is lacking in ccesonia and 
having the dark border of the hind wings of ccosonia lack- 
ing in eurydice. Its female is described as being smaller 
than that of eurydice, but otherwise practically identical 
with it. This case, as Wright has suggested, is a most 
inviting subject for further study, and, judging by what 
he says of the sexual instincts of the eurydice male — '* a 
wooer . . . energetic and persistent, not hesitating to 
ignore all rules of propriety, of species and of genera '' 
— ^not difficult of experimental management. 

The genus Basilarchia, the admiral butterflies, is well 
known for the hybridization of its very unlike species, 
B. arthemis the '* banded purple '' of the northern states, 



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332 THE AMERICAN NATURALIST [VoL.XLVIII 

B. astyanax the '* red-spotted purple '' of the southeast- 
ern states. The hybrid species, B. proserpina, occurs 
in a zone in which their two faunal areas overlap. 
In this same group is the common *' viceroy '' B. ar chip- 
pus, the range of which roughly covers that of both the 
other species and extends further westward, touching the 
Pacific coast in Washington ( Scudder ) . The experiments 
of Edwards, and especially of Field, have shown that 
these three well-differentiated pure species occupying 
contiguous, or in respect to archippus overlapping, 
territory are in some cases at least mutually fertile. 
B. arthemis and astyanax regularly interbreed in the 
narrow zone where proserpina occurs. Proserpina, the 
hybrid, usually shows the general dominance of the 
astyanax characters (lack of white band). 

From eggs laid by a wild female proserpina Edwards^^ 
secured three arthemis, one proserpina. Field^^ raised 
from a similar lot of eggs nine proserpina, seven arthe- 
mis. Presumably in each case the male parent was the 
recessive arthemis, and hence equal numbers of the two 
types would be expected. Field has also succeeded in 
crossing a 2 astyanax with a <? arthemis, and a 2 viceroy, 
archippus, with a c? arthemis, the latter pair producing 
nine males intermediate in color. Specimens of an ap- 
parent hybrid, intermediate in color between astyanax 
and archippus, have also occasionally been captured. 

The complete overlapping of the faunal area of archip- 
pus upon those of the two other species indicates that, 
though crossing sometimes occurs, the resulting hybrids 
are probably usually sterile, though this matter has not 
yet been thoroughly investigated. Proserpina, however, 
is a fertile and extraordinarily variable hybrid. In view 
of its great variability it appears, by the way, not impos- 
sible that archippus, the red-brown *' mimic '' of the mon- 
arch, Anosia plexippus, may have arisen as a mutation 
from the hybrid proserpina, though the wide-spread 

10 Canadian Entomologist, Vol. IX, 1877. 

11 Psyche, Vol. XVII, No. 3, 1910. 



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No. 570] SPECIES-BUILDING 333 

range of archippus at present and our ignorance of the 
state of the Basilarchia stock at the time of the origin of 
the ''mimic'' make any such specific historical guess 
hazardous. It may, however, some time be possible by ex- 
perimental breeding to extract from this red-spotted pur- 
ple hybrid a red-brown type similar to archippus. If the 
Basilarchia stock were as easily bred as Drosophila, one 
might be very confident of accomplishing this. In any 
event, the theory of the origin of mimicry by natural 
selection is, in the opinion of the writer, entirely super- 
fluous, though this celebrated monarch-viceroy case 
should be exhaustively studied by experimental methods, 
to determine whether natural selection now operates in 
any degree in the matter. 

Examples of clusters of interbreeding types may be 
drawn in large numbers from various classes of animals 
and plants. Bateson^^ has recently called attention to the 
interesting case of the two American flickers described 
by Allen,^^ the eastern Colaptes auratus and the western 
and Mexican C. cafer, which hybridize in the zone in 
which their faunal areas overlap, the American grackles, 
the golden-winged and blue-winged warblers and their 
hybrids, Lawrence's and Brewster's warblers, and others. 

In reference to the common purple grackle, which 
Chapman" regards as a hybrid between the Florida 
grackle and the bronzed grackle, Kidgeway^^ says: 

My own opinion in the matter exactly coincides with Mr. Chapman's 
but since so many forms now ranked as sub-species are similarly in- 
volved I prefer, at present, to leave the matter in abeyance. 

This signiflcant statement from a master of ornithologi- 
cal taxonomy indicates that hybridization among Ameri- 
can birds is a promising subject for investigation. 

Of the occasional mutual fertility of unlike strains dif- 
ferent enough to be classed as unquestionable species, 

12 "Problems of Genetics,'' 1913, Chap. VII. 

i^BuU. American Mus, Nat Hist., Vol. IV, 1892. 

" Ibid. 

w Birds of North and Middle America,'' Part 2, p. 219, 1902. 



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334 THE AMERICAN NATURALIST [VoL.XLYin 

there also can be no doubt. '* We can only escape the 
conclusion that some species are fully fertile when 
crossed," wrote Darwin,^® ''by determining to designate 
as varieties all the forms that are quite fertile/' and he 
added that some plants exposed to unnatural conditions 
are so modified '' that they are much more fertile when 
crossed by a distinct species than when fertilized by their 
own pollen. '* 

The rareness of these crosses between unlike strains or 
species and the partial sterility of the offspring are not 
obstacles in the way of regarding occasional hybridiza- 
tion as one of the chief sources of mutation and hence 
eventually of new species, for, as my preliminary experi- 
ments in hybridizing species of C alias have already 
shown, there may exist within a strain of species-hybrids 
certain individuals that ^re fertile, though the most of 
their brothers and sisters, mated, respectively, in a similar 
way, are sterile. Nature probably makes more random 
experiments in hybridization than we imagine ; many fail; 
some succeed; and in especially favorable stock Uke 
Colias, judging from the numbers of closely aUied but 
different types (species) occurring in the same localities 
in western Asia or in northwestern United States and 
British America, probably many succeed. 

In seeking to determine how mutation, whether the re- 
sult of hybridization or of possible climatic influences, 
acts in the production of new species, it is possible from 
cases already at hand to suggest possible steps in the evo- 
lution of distinct, mutually infertile, types from one com- 
paratively simple polymorphic species. 

The well-known dimorphic European currant moth, 
Abraxas grossulariata, in which the light-colored (reces- 
sive) variety, lacticolor, is found in nature only in the 
female sex, will serve as an example of an elementary 
condition. Lacticolor males, as Doncaster*^ has shown, 

16 *' Animals and Plants under Domestication/' Vol. II, Oiap. 19, p. 179. 
IT* 'Report of the Evolution Committee, '* 4, 1908. 



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No. 570] SPECIES-BUILDING 335 

may readily be bred. When one of these males is mated 
with a lacticolor female, there is produced in captivity a 
pure lacticolor strain. If lacticolor males and females 
should be segregated and allowed to breed together until 
they have become as abundant as the typical form, this 
case would then resemble that of the Colorado lady beetles 
of the genus Adalia, described above, in that it would con- 
sist of different types maintaining their identity while 
freely interbreeding with complete fertility. The 
Abraxas complex differs from the Adalia species-cluster, 
however, in the occurrence of sex-linkage in the inheri- 
tance of the lacticolor variety, whereas in Adalia the 
factors for the different color patterns apparently are 
distributed in the gametogenesis of a heterozygous indi- 
vidual without sex-linkage, freely and at random. 

A more advanced stage in evolution is that represented 
by the Basilarchia species-cluster, in which partial steril- 
ity between the viceroy and the two purple species, over 
the faunal areas of which its own overlaps, and the differ- 
ence in geographical distribution between the banded 
purple and red-spotted purple, keep the three elements 
apart. 

By easy stages we may in imagination pass on to 
groups composed of closely allied species which sterility 
and local segregation completely separate from one 
another, groups that probably have arisen from a poly- 
morphic species that has broken up into its constituent 
parts, and thus given rise to new elementary species. 

The dimorphism of Colias differs from that of Abraxas 
in that the color of the rarer type of female can not be 
transferred in the ordinary course of breeding, without 
further mutation, to the male. It is a sex-limited char- 
acter, like the female color pattern in Colias, (i. e., a wide 
dark border broken with spots) and not sex-linked like 
the variety lacticolor of Abraxas. 

The white female of Colias is regularly heterozygous 
for color. She produces as many white daughters as 



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336 THE AMERICAN NATURALIST [Vol 

yellow, or orange, as the case may be. Evidently, i 
to extract a pure white race from C. philodice or ( 
theme, it will be necessary by a mutation to obtaii 
homozygous white female, and then by a further m 
a homozygous white male. White males are kn 
nature as rare aberrations, but, whether they an 
zygous or heterozygous for color, it is impossible 
Among the two thousand offspring of heterozygou 
females of philodice and eurytheme that I ha^ 
since 1908, there has been not a single white mal 
sons of a white female, though some are capable o 
mitting the white, are always yellow or orange, 
lately, however, raised a large brood in which 
females were white. This was a '* back cross '' 1 
a white female of the orange eurytheme and a m; 
cies-hybrid (son of a white mother). Precisely 
matings, however, gave both white and colored 
offspring in equal numbers; hence in the produ( 
this brood there was probably a mutation. Fro 
stock as this the extraction of a pure white ra( 
Colias at some time may possibly be accomplishec 
In this connection it is interesting to note that ^ 
the testimony of a good observer, the late Mr. 
Wright," who made the study of Californian bu 
his life work, to the effect that the white variety oj 
eurytheme ''is now quite common, though twe 
years ago it was a great rarity, and it was accoi 
feat to secure one of them, and if the present rat 
crease of the blond form shall go on, in a few h 
years the normal orange-colored female will be 
and unknown." If this is a fact, and not an illus 
to a general increase in the population of eur 
owing to an increase in the cultivation of the foo< 
alfalfa, in that region, it may be the result of \ 
mutations, whereby homozygous white females m.i 
been introduced into the population. It will be o 

iTLoc. cit., p. 117. 



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No. 570] SPECIES-BUILDING 337 

est to determine whether such true-breeding white 
females actually occur in California. 

Evolution in Colias is usually regarded, on the other 
hand, as tending towards suppression of the white stock 
rather than its further extension, inasmuch as Pieris and 
other allied genera are white. It seems to be a reason- 
able hypothesis that, by progressive mutations in Colias 
affecting first the male then the female,^® white has be- 
come yellow; yellow, orange; orange, red, or a fiery 
orange ;^* or yellow may be transmuted into black, as in 
an aberration of the male in C. philodice. By retrogres- 
sive or degressive mutations, accordingly, we may hope 
to isolate from C. philodice or C. eurytheme a pure white 
race. 

Summary and Conclusions 

The erroneous idea that Linnsean species are homo- 
geneous, well-defined groups of equal importance has 
done much to retard progress in the experimental study 
of evolution. The limits of a species are often arbitrary, 
depending ultimately upon the temperament of the des- 
criber, and frequently based upon ignorance of the near- 
est allies of the individuals described, living in other 
parts of the world. 

The most definite criteria of species, viz., that '' spe- 
cific *' characters are constant, and that hybrids of 
Linnaean species are infertile inter se, are only approxi- 
mately correct. Characteristics of species sometimes 
occur in heterozygous condition. Hybrids of Linnsean 
species, as has long been known, are often fertile. These 
matters, owing to traditional, unwarranted respect for 
described species, have received comparatively little in- 
vestigation. 

Examples of hybridization in Adalia, Colias, Meganos- 
toma, Basilarchia and Paratettix among insects, in Co- 
laptes, Quiscalus, and Helminthophila among birds are 
cited. 

18 In C. dimera of South America, for example, the female is yellow, but 
in the male the /ore wings are orange. 
1* As in the Asiatic eogene. 



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338 TRE AMERICAN NATURALIST [Vol. XLVIII 

Occasional fertile crossing of unlike strains that rarely 
interbreed is a probable source of mutations and new 
types. 

A suggestion is made that a comparatively simple poly- 
morphic species (like Abraxas grossulariata) may break 
up into a cluster of mutually fertile elementary species 
{e. g.y Adalia in Colorado). Further differentiation, in- 
volving partial sterility, may be illustrated by the Basi- 
larchia species-cluster. This may be followed by the 
establishment, and isolation through complete sterility, 
of distinct types, or species in the strict sense of the term. 

Evolution of color in the yellow and orange butterflies 
of the genus Colias involves white, which exists to-day in 
heterozygous condition in certain females. If the an- 
cestors of Colias were white, as in Pierids generally, we 
have only to imagine a mutation in the male-producing 
germ cells of the original white females, by virtue of 
which white pigment was replaced by, or transmuted into, 
yellow. This would make all the males yellow, leaving 
all the females white, which is true of certain arctic 
species to-day. 

A similar mutation affecting the germ cells of these 
white females, but introducing the factor for yellow into 
only half of them, would produce the heterozygous condi- 
tion found in C. philodice and C. eurytheme. Pure yel- 
low strains may readily be bred from such mixed stock, 
and hence, probably, it has come about that four fifths or 
nine tenths of the females of C. philodice in eastern 
United States are pure yellow. 

Progressive mutations from yellow to orange and fiery 
orange, affecting first the male, then the female, have 
probably occurred in Colias in many part of the world, 
especially in warmer climates. Climatic conditions deter- 
mine the amount of orange pigment in the cross between 
the orange eurytheme and the yellow philodice. This 
hybrid is larger and contains more orange when raised in 
summer than when bred in late fall and winter. C. philo- 
dice in this cross is a Mendelian recessive. 



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HEREDITY OF BRISTLES IN THE COMMON 
GREENBOTTLE FLY, LUCILIA SERICATA 
MEIG. A STUDY OF FACTORS GOVERN- 
ING DISTRIBUTION^ 

PHINEAS W. WHITING 
BussET Institution 

In a previous paper^ I have given data showing that 
variation in the number of posterior dorso-central and 
acrostichal bristles of the common greenbottle fly, Lucilia 
sericata Meig., is determined by hereditary factors. 
Since the publication of that paper further evidence, 
bearing upon the nature of the hereditary factors in- 
volved, has been obtained. 

Two general conclusions from the work may be stated 
as f oUows : 

1. Reduction in bristles tends to affect the males more 
than. the females, while additional bristles are found more 
often in the females. 

2. Distribution as well as number of bristles is heredi- 
tary. 

On account of very high mortality in these flies it has 
been impossible to make selections as might seem desir- 
able. The results, however, furnish considerable evi- 
dence for the foregoing conclusions, and throw light, I 
believe, on the nature of factors governing distribution, 
such as spotting factors, for example. 

Fig. 1 shows the mesonotum of Lucilia sericata with 
chaetotaxy normal. The bristles considered in my work 
are those lettered A, B, C, the post-acrostichals, and A\ 
B\ C, the post-dorso-centrals. 

1 Prom the Entomological Laboratory of the Bussey Institution, Harvard 
University, No. 77. 

2 Whiting, P. W., "Observations on the Chaetotaxy of Calliphorin®, " 
AnncUs of the Entomological Society of America, VI, 2. 

339 



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340 THE AMERICAN NATURALIST [VoL.XLVm 




riQ. 1. 

It is evident that these bristles form a group of twelve 
in four rows of three each. 

This arrangement is recorded as 3, 3, 3, 3, the separation into rows 
being denoted by commas. 

When one or two of the anterior bristles of a row are omitted, the row 
is denoted by 2 or 1, respectively. 

In order to denote the omission of the second or third bristle wh«i 
those anterior to it are not omitted, the normal positions of the bristles 
are recorded as a, b, c, from anterior to posterior. Thus a row lacking 
the second bristle would be called ac. 

Addition of a supernumerary bristle ijito a row is denoted by ! in- 
serted in the proper position between or in front of the letters denoting 
the normal bristles. Thus addition of a bristle in front of a row would 
be expressed by calling the row !abc. 

Insertion of a supernumerary bristle between the normal rows is 
denoted by parentheses enclosing a, b, or c, acording to the position 
of the bristle from anterior to posterior. Thus a definition as 3, (a), 
3, 3, 3, would denote the addition of a bristle between the first left post- 
dorso-central and the first left post-acrostichal. 

Additional bristles are usually smaller than the normal, but range all 
the way from microchaetae to the size of the normal macrocluetflB. A 
small bristle is denoted by italics. 

The progeny of a few wild females have been bred and 
counted since my previous paper.^ These have been 



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No. 570] FACTORS GOVERNING DISTRIBUTION 



341 



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342 THE AMERICAN NATURALIST [Vol/XLVHI 

averaged with those recorded previously and the results 
given in Table I. 

From this table it appears that progeny of normal 
mothers show a certain degree of variation in the direc- 
tion both of loss and of acquisition of bristles ; progeny 
of reduced mothers tend more toward reduction; and 
progeny of mothers bearing additional bristles tend more 
toward the addition of bristles. It is also evident that in 

3 It is thought desirable to put on record a detailed account of these fam- 
ilies as they furnish in themselves a few points of interest. This record is 
given below with the exception of the progeny of 1913-^, discussed in a 
later part of this paper. 

1913-5, L. sericata ? = 3, ab, ab, 3, taken at Bussey Institution, May 6, 
1913, gave 

11(J(J = 3, 3, 3, 3. 
1 c? = 3, 3, 3, 2^ 

3c?c? = 3, 2, 3, 3. 17 $9 = 3, 3, 3, 3. 

1 cf=3, 3, ac, 3. 1 5 = 3,2,3,3. 

1913-C, L. sericata ? = 3, 3, 2, 3, taken at Bussey Institution, May 6, 
1913, gave 

49c?(?=3, 3, 3, 3. 5705 = 3, 3, 3, 3. 

1 ^ = 3, 3, abc, 3. 1 ?= -'abc, a /be, 3, 3. 

1 ^ = 3, albc, albc, 3. 1 ? = 3, a/bc, 3, 3. 

1 c? = 3, a.'bc, 3, 3. 
1 c? = 3, !abc, 3, 3. 
In this case I attribute the additional bristles to the combination of fac- 
tors introduced by the male. An example of this sort in which a reduced 
female produces offspring abnormal predominantly by addition is very un- 
usual. There are, however, occasionally flies with extra bristles in reduced 
strains, a fact which may be explained by recombinations of factors or by 
mutation. 

1913-F, L, sericata ? = 3, 3, 3, 3, taken at Bussey Institution, March 19, 
1913, gave 

24c?c? =3, 3, 3, 3. 19?? = 3, 3, 3, 3. 

from a mating of these were produced 

92cfc? = 3, 3, 3, 3. 89?? = 3, 3, 3, 3. 

1 <J = 3, 3, albc, 3. 1 ? = 3, albc, 3, 3. 

1913-1?, L. cwsar ? = 3, 2, 2, 3 (the chaetotaxy normal for this species), 
taken at Bussey Institution, May 5, 1913 gave 

55c?(? = 3, 2, 2, 3. 34?? = 3, 2, 2, 3 

4c?c? = 3, 1, 2, 3. 1 $ = ac, 2, 2, 3. 

1 cJ = 3, 2, b, 3. 

2<?(?=3, 1, 1, 3. 

1 c? = 3, 2, 1, 3. 

1 cJ = 3, b, 2, 3. 
The flies of this mating are not averaged with the others, as it is possible 
that this species may be different in its variability from L, sericata. It is 
noteworthy, however, that here also reduction favors the male more than 
the female. 



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No. 570] FACTORS GOVERNING DISTRIBUTION 343 

general reduction tends considerably to favor the males, 
while addition favors the females to a slight extent. 

In my previous paper (p. 264) is given in detail a 
record of the progeny of a female L. sericata (1912-c) 
lacking both of the first and the right second post-acros- 
tichal (3, 2, 1, 3). These were inbred to the third gen- 
eration, in all cases brother being mated with sister in an 
attempt to analyze the stock as thoroughly as possible 
and to reduce heterozygosis of factors.* Here again, due 

« Mr. Harold D. Fish has kindly furnished me the following note : 

''The importance of mating sisters with brothers for a long series of 
generations in the experiments aimed to detect Mendelizing units of inherit- 
ance and analyze groups of them, quite generally seems to have been over- 
looked. As first shown by Castle ('03), random mating of the individuals 
of successive generations beyond F^ tends to produce in each generation a 
population with the same per cent, of homozygosis and heterozygosis as is 
present in the F, generation, i, ^., 25 per cent, of the individuals are homozy- 
gous for. one factor of a given allelomorphic pair, 25 per cent, homozygous 
for the other factor, and 50 per cent, heterozygous for both. Such a system 
of random matings often has been confused with the more restricted system 
of mating sisters with brothers. 

**It is evident that if A and B are an allelomorphic pair the F, zygotes, 
resulting from a mating of AA with BB, will be AA, 2AB and BB. 
Further, if these are all females and are mated in all possible ways with the 
same number and kinds of males, one sixteenth of the matings will be AA 
with AA, and one sixteenth will be BB with BB, One eighth of the matings, 
then, will be homozygous and produce only homozygous young, which, be- 
cause of the restricted system of mating only sisters with brothers, will pro- 
duce, in turn, only homozygous matings. The remaining matings, seven 
eighths of the total, will produce various proportions of homozygous and 
heterozygous offspring and matings. It is rather natural to assume that one 
eighth of these matings will be homozygous and seven eighths heterozygous. 
This would mean that the proportion of heterozygous matings between indi- 
viduals of the Fh generation would be (7/8 )*»"*. Accordingly one would ex- 
pect an automatic increase in homozygosis. The expectation is justified al- 
though the figures are misleading. 

"Dr. Baymond Pearl first published the figures exactly expressing the 
per cent, of automatic increase in homozygosis for patred allelomorphs, under 
the restriction of mating only sisters with brothers. This article appeared 
in the January, 1914, number of the American Naturalist. It is a correc- 
tion of his paper in the October, 1913, number of the same periodical, in 
which he states in no uncertain terms that an automatic increase in homo- 
zygosis in obligate bisexual forms is impossible. When I read the October 
paper I was naturally much surprised, since, nearly a year before, during 
conversation with Mr. Whiting, the increasing per cent, of homozygous 
matings resulting from successive matings of sisters with brothers had been 
discussed. Of course, the per cent, of individuals in any generation, which 
are homozygous for one or the other of a pair of allelomorphs, is the same 



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344 THE AMERICAN NATURALIST [Vol. XLVIH 

to high mortality, selection as might have been desired 
has been impossible. 

A detailed account of this strain is given in Table II. 
In recording any mating of this strain the letter c denot- 
ing the entire strain, is followed by Fi, Fg, etc., denoting 
the generation from which the mated flies have been 
chosen. This symbol is then followed by a, b, or c, denot- 
ing the first, second, or third mating, respectively, of the 
generation indicated. Thus mating cFgb is the second 
mating of the second inbred generation of strain 1912 — c. 
This method of recording matings has been followed 
throughout my work. 

Several points of interest are to be noted in this strain 
but it is thought best to present the remaining data on 
reduced strains before proceeding to a discussion of this 
matter. 

Strict inbreeding has been followed in the strain re- 
corded below. In no case have there been either cousin- 
matings or outcrossings. 

1913-^, L. sericata ? = 3, ac, ac, 3, taken at Bussey Institution, Forest 
Hills, Mass., May 6, 1913, gave 

96c?c?=3, 3, 3, 3. 129?? = 3, 3, 3, 3. 

1^5 = 3, ac, ac, 3. 1 ?=3, ac, 3, 3. 

2c?cf = 3, ac, 3, 3. 2?? = 3, 2, 3, 3. 

2(?c? = 3, 3, ac, 3. 
1 c? = 3, 2, ac, 3. 
4c?c? = 3, 2, 3, 3. 
3c?c? = 3, 3, 2,3. 

as the per cent, of the allelomorphic factors which are homozygous in the 
average individual of that generation. Because Br. Pearl in his October 
paper referred frequently to the paper by Dr. E. M. East ( '12) on "Hetero- 
zygosis in Evolution and Plant Breeding. *' I gave Dr. East my figure ex- 
pressing the per cent, of homozygosis in successive generations resulting 
from matings of sisters with brothers. Dr. Pearl's correction followed a 
letter from Dr. East which pointed out the error of applying the mathe- 
matics of random matings in each generation to a case where sisters always 
had been mated with brothers. The percentages, as computed, were pub- 
lished by Dr. Pearl for the following generations: Pi — 100 per cent., Fx — 
per cent., F^ — 50 per cent., F3 — 50 per cent., F* — 62.5 per cent., F^ — 68.25 
per cent., Fo — 75 per cent., F, — 79.687 per cent., Fg — 83.594 per cent, F, — 
86.719 per cent., Fjo — 89.258 per cent. Previous to giving these figures to 
Dr. East I computed the number of generations necessary to reduce heterozy- 
gosis to less than one half of one per cent, and found this condition first 
realized in the F^s generation, which is 99.553 per cent, homozygous. The 
importance of these figures in work of this nature is quite obvious. * * 



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No. 570] FACTORS GOVERNING DISTRIBUTION 



346 



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346 



THE AMERICAN NATURALIST i^ 



F. 



from^F.a={|-||«.33.33- 



• 24 


cfd' = 3, 3, 3, 3. 


53??: 


= 3, 3, 3, 3 


11 


fJJ=:3, ac, ac, 3. 


2?$; 


= 3, ac, ac. 


13 


c?cf = 3, ac, 3, 3. 


52?' 


= 3,3,ac, 3 


9 


d'cf = 3, 3, ac, 3. 


1 ?: 


= 3, ac, Abe 


2 


(}(J=z3, a6c, ac, 3. 


1 ?: 


= 3, ac, 2, 3 


1 


.^ = 3, 3, a6c, 3. 


2?? 


= 3, 3, a6c, 


1 


(? = 3, 1, 1, 3. 


1 ?: 


= 3, a6c, 3, 


3 


c^c^ = 3, ac, 2, 3. 


1 ?: 


= 3, a6c, 2, 


5 ^^ = 3, 2, ac, 3. 


2??: 


= 3, 2, 2, 3 


1 


cr = 3, 2, 2, 3. 


1 ?: 


= 3, 3, 2, 3 


5cfdr = 3, 2, 3, 3. 


1 ?: 


= 3, 3, a//c 


2, 


cfc? = 3, 3, 2, 3. 


1 ?: 


= 3, a!bc, 3 


1 


^ = 3, ace, 3, 3. 






from -4F,a = c? and ? = 3, 


ac, ac, 3. Pair segregated Ji 


July 25. 






c?c? 


?? 


(?(? 


?2 


6 


35 = 3, 3, 3, 3. 


7 


2=3, 2, a 


42 


18 = 3, ac, ac, 3. 


10 


4 = 3, 2, 1 


9 


18 = 3, ac, 3, 3. 


7 


7 = 3,2, J 


16 


12 = 3, 3, ac, 3. 


5 


7 = 3, 3, i 


5 


2 = 3, ac, 2, 3. 


1 


= 3, ac, 


from ^Fjft = 






c? = 3, ac. 


,2,3. 






S=3, a6c, 2, 3. 






Pair segregated July 12; larvae 


July 25. 




c?c? 


5? 


(?(? 


22 


16 


45 = 3, 3, 3, 3. 


4 


1 = 3,3, 2 


34 


9 = 3, ac, ac, 3. 





1 = 3, a6c 


8 


9 = 3, ac, 3,3. 





3 = 3, 3, I 


7 


11 = 3, 3, ac, 3. 





3 = 3, a6c 


. 8 


= 3, ac, 2, 3. 


1 


= 3, b, 3 


9 


1 = 3, 2, ac, 3. 


1 


= 3, ac. 


3 


= 3, 2, 2, 3. 





1 = 3, a6c 


2 


1 = 3,2,3,3. 






^from^F.a={|;3,ac,a,: 


5, from AT^. Pair segregated 
3, larvsB August 20. 


c?c? 


52 


(?(? 


22 


6 


32 = 3,3,3,3. 


4 


7 = 3,2,3 


24 


11=3, ac, ac, 3. 


1 


5 = 3,3, 2 


4 


20 = 3, ac, 3, 3. 


1 


= 3, ac, 


6 


13 = 3, 3, ac, 3. 





1 = 3, ac. 


9 


6 = 3, ac, 2, 3. 


1 


= 3, ac, 


6 


7 = 3, 2, ac, 3. 





1=2,2,2 


3 


4 = 3,2,2,3. 





1=3, 3, a 


from ^F,6 = c? and 9 = 3, 2, 


ac, 3, from A¥^, 


Pair segreg 


13; larv8B August 20. 






c?cf 


29 


c?cf 


52 





18 = 3, 3,3,3. 


13 


2 = 3, 2, a 


10 


3 = 3, ac, ac, 3. 


6 


2 = 3, 2, 2 


4 


5=3, ac, 3, 3. 


1 


7 = 3,2,3; 


1 


2 = 3, 3, ac, 3. 


1 


4 = 3,3,2, 



13 3 = 3, ac, 2, 3. 

from ATiC=:f} and 2 = 3, 2, 2, 3, from ^F^. Pair segreg 
13; larva? August 25. 



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No. 570] FACTORS GOVERNING DISTRIBUTION 



347 



6 15 = 3,3,3,3. 2 15 = 3,2,3,3. 

10 7 = 3, ac, ac, 3. 3 8 =: 3, 3, 2, 3. 

11 7 = 3, ac, 3, 3. l = ac, 1, 2, ac. 
10 12 = 3, 3, ac, 3. 1 = 3, 2, ace, 3. 

8 3 = 3, ac, 2, 3. 2 1=3, ace, ac, 3. 

7 7 = 3, 2, ac, 3. 1 = 3, ace, 3, 3. 
5 4 = 3,2,2,3. 

from ATffil = ^ and 2 = 3, ac, ac, 3, from A¥^, Pair segregated August 

13; male died August 18 and another with same chaetotaxy put in; larvse 
September 1. 

(fcf 22 (f(f 22 

3 = 3,3,3,3. 1 1 = 3, ac, 2, 3. 

1 2 = 3, ac, 3, 3. , 1 = 3, 3, aabc, 3. 
1 1 = 3, 3, ac, 3. 

The record of 1913- A, recorded in tabular form is given in Table III. 

We are now in a position to consider the nature of re- 
duction of bristles in Lncilia sericata. 

It is evident from Table t (record of first generation 
flies), that reduction and addition of bristles are both 
hereditary. It is further evident from Table III, (inbred 
strain), that reduction yields readily to selection. This 
eflFect may be expressed by making the number of bristles 
lost the numerator of a fraction of which the denominator 
is the number of bristles normal. We then have a ratio 
for each generation of 1913 — A as follows : 



Fi 



18 
2892 



= 0.006 =*= .010, 



^' ' 1788 " ^'^^^ ^ -^^^ 



435 
^* ■ 4692 = ^-^^ * •^^' 

^4 • TT?k = 0.104 =«= .003. 



It may be readily seen by glancing at these figures that 
selection has a very rapid eflfect. It also appears that as 
we pass from Fj to F4 the effect of selection gradually 
diminishes. This may be expressed by dividing the above 
decimals for each generation by that of the preceding 
generation. 



Fi 



0.055 
0.006 



= 9.16, 



1} 
F2 



0.093 
0.055 



= 1.69, 



F» 



0.104 
0.093 



= 1.11. 



The reason for this decrease in the effect of selection in 
the later generations is that as the selection advances the 
majority of the flies become reduced in two bristles only. 



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348 



THE AMERICAN NATURALIST [VoL.XLVm 



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No. 570] FACT0B8 GOVEBNING DISTRIBUTION 349 

Barely does a fly occur lacking more than two. In the few 
cases in which three or more bristles are lacking, the 
absence of the third acrostichals or of the dorso-centrals 
is as frequent as the absence of first and second acros- 
tichals. Why this should be is difficult to understand, as 
it would be expected that both first and both second post- 
acrostichals might frequently be lacking in the same fly, 
especially as flies asymmetrical for the loss of these 
bristles are common. 

A further point of interest lies in the fact that not only 
is number of bristles a hereditary matter, but their dis- 
tribution is also hereditary. Thus from Table I (first- 
generation flies) we see that in general the first post- 
acrostichals tend to be reduced more than the second. 
This may be expressed as a fraction : 

First post-ac r osticha ls lacking 40.5 _ ^ . q 

Second post-acrostichals lacking 34 

It is possible that thig tendency to reduce the first post- 
acrostichal more than the second is evidence of relation- 
ship to L. ccesar Linn., in which the absence of the former 
and the presence of the latter is the normal condition. 
Strain 1913 — A (Table III), however, gives 

First post-acrostichals lacking __ 329 _ ^ . « 
Second post-acrostichals lacking 750 

Considering the rieduction in the first post-acrostichals 
separately, we may express the effect of selection as 
follows : 



Parents. 
Matings. 


l8t 


post-acros. 
lacking. 


Offspring. 
First post-acros. lacking. 
First post-across, normal (2 per fly) 


A 




0(f) 


^ = 0.021 ±.004. 


AF^a 




1 


|«g = 0.087 ±. on. 


AF^ 







-S^ = 0M1±.002. 


AF,b 




2 


r\ = 0.093 ± .010. 
356 



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350 



THE AMEBIC AN NATURALIST [VoL.XLVm 



AF^ 
A¥nb 
AFtC 



64 
346 

60 
190 

74 
292 



= 0.185 ±.014. 
= 0.316 ± .023. 
= 0.253 ±.017. 



From these figures it is readily seen that reduction m 
the first post-acrostichals is not entirely consistent with 
the direction of selection. 

Let us test the same matter for reduction in the second 
post-acrostichals. 



Parents 
Matings 

A 

AF^a 

AF^ 

AFJb 

AF^a 

AFJ> 

AF^ 



1st post-acros. 
lacking 

2(f)' 

1 
4 
1.5 



Offering. 

First post-acro s. lacking^ 

First post-acros. normal (2 per fly) 



8 



482 
63 



: 0.01 7 ±.004. 



298 
193 



= 0.211 ±.016. 



426 

147 



= 0.453 ± .016. 



356 

145.5 



= 0.413 ±.018. 



= 0.420 ±.179. 



346 



^^ = 0.363 ± .023 



190 
108 



= 0.370 ±.019. 



In this case also the results are not consistent witti the 
direction of selection, although there is better agreeuaent 
here than in the case of the first post-acrostichals. Ibis 
is probably due to the fact that the numbers are larger. 
As regards the irregularities that do occur, I consider 
them as evidence of recombinations of multiple factors, 
insofar as they are not due to probable error. 

1912 — c (Table II) is a strain that especially tends to 
lack the first post-acrostichals. Thus for the entire 
strain 

First post-acrostichals lacking __ 25 _ 
Second post-acrostichals lacking "" 11 ~ 



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No. 570] FACTORS GOVERNING DISTRIBUTION 



361 



In the 137 offspring of a single mating of this strain, cF^c, 
there are 23 first post-acrostichals lacking, showing that 
it is due to this mating especially that the strain is so 
lacking in first post-acrostichals. 

It can not as yet be said that the factors governing the 
first post-acrostichals are altogether independent of those 
governing the second. That a. certain degree of inde- 
pendence obtains is evident from a comparison of the 
ratio of reduction in first to reduction in second post- 
acrostichals in flies in general (Table I), with the same 
ratio for strain 1913 — A. In the former case we have 
40.5/34 or 1.19. In the latter we have 329/750, or 0.43. 
In order to establish the independence of the factors un- 
derlying these two tendencies it will be necessary to 
obtain, either by selection from a strain showing both 
tendencies or by breeding from wild stock, two strains, 
one tending to lack the first while retaining the second, 
and the other tending to lack the second while retaining 
the first. 

A point of interest in strain 1913—^ is the presence of 
twelve small second post-acrostichals in the progeny of 
AFzb in which the female had one of these reduced to half 
size. The progeny of AFza in which there was total ab- 
sence of these bristles showed either presence or absence 
of the same but no reduced bristles. In Fj, however, we 
have eight reduced bristles. The occurence of these 
small bristles in the progeny of certain matings is taken 
as an indication of recombinations of multiple factors, 
but the numbers are too small to establish this with cer- 
tainty. 

A glance at the tables shows that third post-acrosti- 
chals are rarely lackhig. These are normally present in 
all related species, while in a few, — Cynomyia mor- 
tuorum, Musca domestica, Pseudopyrellia cornicina, and 
others, there is normally but one post-acrostichal, and this 
is always the last. 

Posterior dorso-centrals are very rarely absent. Thus 
in the 2,273 flies recorded in Table I only one had a single 
post-dorso-central missing. Reduction in post-acrosti- 



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352 THE AMEBIC AN NATURALIST [Vol. XLVIH 

chals among these is 79.5. Among the 1,206 flies of strain 
1913 — A there are but three post-dorso-centrals gone. 
This latter is a highly reduced strain as regards post- 
acrostichals, lacking 1,081. This great reduction in 
acrostichals seems not appreciably to have affected the 
dorso-centrals, a fact which argues for the independence 
of the factors controlling the distribution of these two 
sets of bristles. 
Thus for flies recorded in Table I we have 

Post-acrostichals lacking _ 79.5 _ ^ ^^ 
Number of FH^ " 2273 ^ ^'^^' 
One post-dorso-central lacking. 
For flies in strain 1913—^ (Table III) we have 

Post-acrostichals lacking ^ 1081 _ ^ qq 

Number of Flies " 1206 ~ ^'^^' 

Three post-dorso-centrals lacking. 

Among the 3,238 flies recorded in Tables I and in only 
four post-dorso-centrals are lacking, while among the 810 
flies of strain 1912 — c (Table II) there are 13.5 lacking. 
The lack of post-acrostichals in this latter strain is 37. 
There are 9.5 dorso-centrals lacking in the progeny of the 
trio, cFga, among which there are only seven post-acros- 
tichals lacking. 

Thus we see that lack of post-dorso-centrals is in no 
way correlated with lack of post-acrostichals, but is evi- 
dently governed by distinct factors. 

Variatiois by Addition of Bristles 
A strain of Lucilia sericata, 1913 — E, showed some 
interesting variations chiefly in the direction of addition 
of bristles. The mother was normal (3, 3, 3, 3), taken at 
the Bussey Institution, March 19, 1913. The detailed ac- 
count of the strain follows : 

c?cf ?? 

38 43 = 3,3,3,3. 

1 = 3, 3, able, 3. 
F, 



from ^F.a={^ = 3;3^ab!c,3. 



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No. 570] FACTORS GOVERNING DISTRIBUTION 35S 



C?(f 


S? 






69 


76 = 3, 3, 3, 3. 
= able, 3, 3, 3. 






1 









l=!abc, 3, 3, labc. 






F, 

from EF^=Z(J and 2 = 3, 3, 3, 3. 






cfcf 


S? 


(?C? 


SS 


318 


251 = 3,3, 3, 3. 


4 


5 = 3, albc, 3, 3. 


13 


61 = !abc, 3, 3, !abc. 





1= lalbc, 3, 3, labc. 


1 


4=!abc, 3, 3, 3. 


1 


= 3, abcl, abcl, 3. 
0=labc, albc, albc, la 


6 


6 = 3, 3, 3, labc. 


1 


1 


3 = 3 (a), 3, 3, 3. 





l=labc, albc, 3, labc 


5 


2 = 3, 3, 3 (a), 3. 


1 


= 3, able, 3, 3. 


3 


5 = 3, 3, albc, 3. 


1 


l = albc, 3, 3, albc 


1 


= 3, albc, abcl, 3. 





3= labc, 3, 3, lalbc 


1 


= 3, 3, 3, albc 





1 = 3, albc, 3, labc 


1 


= 3, 3, 3, able. 





l=labc, 3, 3 (a), labc 


1 


0=!abc, a!bc, 3, 8. 





1= labc, albc, 3, lalbc 


1 


= 3, 3, 3 (b), 3. 





l = albc, 3, albc, albc 


1 


1 = 3, albc, albc, 3. 


1 


0=lbc, 3,3, lalbc 


1 


0=lalbc, lalbc, !a!bc, lalbc 


1 


= 3, 3, 2,3. 





1 = 3 (b),3, albc, albc. 
2= lalbc, 3, 3, labc. 


1 


= 3, ac, 3, 3. 





1 


= 3, ac, ac, 3. 



F. 

from . 


1 = labc, 3, albc, labc. 





1 = 3, abc, 3, 3. 


rro - f ^^^ 3, 3, 3, 3. 

^•«- is =3; 3; albc, 3. 






Pair 


segregated, July 22: larvae July 30. 




dd 


S? 


c?c? 


?? 


191 


100 = 3,3,3,3. 


1 


0= labc, 3, abcl, labc 


25 


43= labc, 3, 3, labc. 


2 


= 3, abcl, 3,3. 


4 


3= labc, 3, 3, 3. 


1 


0=labc (a), 3,3. 





1 = 3, 3, 3, labc. 


1 


= 3 (a), 3,3 (a), 3. 





1= labc, albc, 3, labc. 


1 


l=labc, 3, 3 (a), labc 


1 


2= labc, 3, albc, labc. 





l=lbc, 3, 3, 3. 





2= labc, albc, albc, labc. 







from .FF,6=<J and $ = 3, 3, 3, 3. Pair segregated August 22. 

cSd 52 c?c? 9? 

41 57 = 3, 3, 3, 3. 2 = 3, albc, 3, 3. 

1 = 3, albc, 3, labc 1= labc, 3, 3, labc 

1 = 3, abcl, 3, 3. 1 = labc, albc, albc, labc 

A summary of this strain is given in Table IV. 

The points of interest to be noted in this table are as 
follows : 

There are many supernumerary bristles in the flies of 
this strain. 

The number of bristles added in the progeny of any 
mating is very variable and has no consistent relation to 
the visible character of the parents. 

Addition of bristles tends very much to favor the 
females, reduction still affecting the males. 

Despite the high ratio of bristles added, there are 



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364 



THE AMEBIC AN NATURALIST [Yoh. :S^x,^yj\S5^ 



3 



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at 

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No. 570] FACTORS GOVERNING DISTRIBUTION 355 

nevertheless a few flies in the strain in which bristles are 
lacking. 

Bristles normally present may be lacking in individuals 
having additional bristles. 

Genebal Summaby and Conclusions 

Taking a general summation of all the bred material of 
Lucilia sericata, we find that reduction affects the males 
while addition affects the females. Of the 5,367 flies bred, 
2,708 are males and 2,659 are females, giving practical 
equality. 

Eeduction in the males is 748.5 bristles, while in the 
females it is only 455.5 bristles. As has been noted before 
the degree of reduction in the females is increased by the 
later generations of strain 1913 — A, by reason of the fact 
that reduction rarely goes beyond the loss of two bristles 
in a single fly. Thus when most of the flies of a popula- 
tion become reduced to this extent it is evident that reduc- 
tion in the males would be but slightly in advance of that 
in the females. 

There are 210 bristles added in the males, while there 
are 343 added in the females. Thus addition affects the 
females more than the males. These figures for bristles 
added represent number of bristles, and thus no distinc- 
tion is made between bristles of large and bristles of 
small size. 

I wish to express my appreciation for the advice and 
criticism offered me in this work by Professor W. M. 
Wheeler, Messrs. H. D. Fish, S. G. Wright, and C. C. 
Little. 



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PHYSIOLOGICAL CORRELATIONS AND CLI- 
MATIC REACTIONS IN ALFALFA 
BREEDING^ 

GEO. F. FREEMAN 
Arizona Agricui/tural Experiment Station 

Climatic Reactions 

To the worker who attempts to apply the recognized 
laws of heredity to the actual operations of plant improve- 
ment many difficulties arise which heretofore have been 
largely avoided by students of pure genetics. Color and 
form characters are but little affected by the immediate 
ordinary environment and hence, for the sake of simplic- 
ity, are usually chosen by investigators of heredity. To 
the economic breeder, however, such characters are of but 
little consequence except in so far as they indicate phyletic 
relationships. Of greater importance to the breeder are 
those differences in yield and quality which are the re- 
sults of inherited, invisible, physiological powers within 
the plants, whereby each variety may respond differently 
in manner or degree to the same environmental stimulus. 

Those hereditary units which have to do with vegetative 
vigor, heat, cold and drought resistance, time of maturity, 
chemical structure, reproductive strength, etc., are as yet 
but little understood. This is largely due to the difficulty 
of exact experiments concerning them. This difficulty is 
occasioned by the complexity of the reactions of these 
hereditary forces with the external environment, and also 
by the direct influence of the development of one part of 
the plant upon that of some other part The plant at ma- 
turity presents the resultant of its environmental reac- 
tions during development. The nature of these reactions 

1 Bead before the American Breeders ' Association, Columbia, S. C, Jan- 
uary 26, 1913. 

356 



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No. 570] ALFALFA BREEDING 357 

is determined by the structure of the vital forces within. 
These differences in vital structure may or may not be 
accompanied by visible morphological differences. Such 
cases of correlation have been known and used in selecting 
for qualities which they were thought to indicate. The 
much quoted example of the supposed correlation between 
the short-haired rachilla and high brewing quality in bar- 
ley is a case in point. It has been found, however, that, 
whereas, in one strain or race the correlation may hold, in 
another, the two characters are in no way related. 
Another case of similar nature is the coupling of cob and 
pericarp color in certain varieties of com and their com- 
plete independence in others. Many other examples could 
be adduced to show that the coupling of two characters in 
a given race of plants is no indication that these same 
characters are inseparably linked in all races of the same 
species. These facts have greatly reduced the value for- 
merly ascribed to gametic correlations in plant breeding. 
Under our present knowledge, therefore, we must depend, 
for the most part, upon direct experimentation, rather 
than correlations, to discover the hereditary physiological 
characters of the varieties with which we are working. 
Any additional light, therefore, which may be had con- 
cerning the nature of such characters, together with meth- 
ods for the study of the behavior of the same in their rela- 
tion to each other and to their physical surroundings, will 
have not only a scientific value, but will also fill a distinct 
practical need. 

As an illustration of such a study we may now examine 
the data concerning the development, yield and chemical 
composition of forty-four regional varieties of alfalfa 
which were grown on the Experiment Station Farm at 
Phoenix, Arizona, during the season of 1910. In the case 
of this plant, which occupies the ground throughout the 
year and from which six or seven crops may be harvested 
during the growing period, the climatic factors include a 
long series of variations coincident with the changing sea- 
sons. Now, since every variety consists of its own pecul- 



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358 



THE AMERICAN NATURALIST [Vol. XLVHI 



iar complex of hereditary physiological forces, each sensi- 
tive in its own manner and degree to the impinging ex- 
ternal stimuli, it is not surprising that the resultant (the 
gross climatic reaction) should be sharply different in the 
several varietal groups. 

The unequal effects upon the vegetative growth of the 
different varieties brought about by the climatic changes 
which occurred during the course of the summer may be 
exhibited by calculating the place variation in yield. This 
is best shown by correlating the first with each of the fol- 
lowing cuttings throughout the season. The result is a 
definite curve, beginning and ending high with a strong 
sag in the middle. 

TABLE I 

Place Variation in Yieli> 

Cattingi 1 and 2 1 and 3 1 and 4 1 and 5 1 and 6 

Correlation. + .75 ± .04 + .68 ± .05 + .33 ± .09 + .36 ± .09 + .58 ± .07. 

These figures indicate the presence of some disturbing 
factor which reached its maximum intensity during the 
fourth and fifth cuttings, and to which certain plots were 
more sensitive than others. The average period through 
which the growth of these two crops extended was June 22 
to August 27. The fact that these dates include the hottest 
portion of the summer strongly suggests temperature as 
the disturbing factor. 

The mean maximum temperature, mean minimum rela- 
tive humidity and the correlation between yield and water 
supplied are given in the following table : 



TABLE II 
Temperature, Relative Humidity and Water Supply 



Cutting 



Dates locIudlDg Arerage Periods 
of Growth 



From March 23 to April 23 
From April 23 to May 23 
From May 23 to June 22 
From June 22 to July 23 
From July 23 to August 27 
From August 27 to October 5 



Mean Max- iMeaDMioimum 
imum Tempera- 1 Relative 
ture o F. I Humidity 



82.8 
93.8 
103.6 
104.8 
104.4 
102.0 



27.00 
23.00 
20.40 
25.26 
30.00 
25.18 



Correlation 

Between Yield 

and Water 

Supply 



— .09±.10 
4- .05 dr. 10 
4 .40 i. 09 
-f .21 ±A0 

— .04 dr. 10 



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No. 570] ALFALFA BREEDING 359 

That the relative humidity had little to do with yield is 
shown by the fact^iat the highest averages for this factor 
occurred on the first and fifth cuttings which were the 
highest and lowest in yield, respectively. 

Although it was intended to give each plot approxi- 
mately the same amount of water for each cutting, uneven- 
ness in tiie slope made this impossible. The average 
amount of water applied to each cutting was 6.28 inches 
with an average standard deviation of 1.54 inches. Now, 
taking cognizance of this variation in the water supply, 
we find that its effect upon the yield was only appreciable 
in the fourth and fifth cuttings. Eecords were not made 
of the water supplied to the first cutting, but after that 
time they are complete. By reference to Table 11 it will 
be observed that these correlations in the second, third 
and sixth cuttings are so small as to be negligible, but in 
tiie fourth and fiftb cuttings they are suflSciently large to 
indicate that this factor was of some importance in gov- 
erning the yields. These results may be interpreted as 
meaning that approximately 6.28 inches of water were 
ample for each cutting during the cooler weather of spring 
and fall. That too much was not given at these seasons, 
however, is shown by the absence of large minus correla- 
tions. Factors other than water supply, therefore, gov- 
erned the yields during these i>eriods. Hot, dry weather 
came on during the growth of the third cutting, but the 
amount of water supplied plus the winter and spring sur- 
plus left in the soil was ample to mature the crop. With 
the continued high demand for water during the hot 
weather of July and August, the surplus having been 
exhausted and the summer rains helping but little, six and 
one fourth inches was not suflScient. There was, therefore, 
marked suffering for water, which was reflected in the 
yields of those plots that received slightly more or less of 
irrigation than the others. 

It would seem, therefore, that high temperature and a 
slight deficiency of water were the disturbing factors in 



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360 THE AMERICAN NATURALIST [Vol. XLVm 

the relative yields of the varieties tested, and that certain 
ones were more sensitive than others to these influences. 

If we turn to the relation between stand and yield, we 
shall again find a strong disturbance of the normal corre- 
lation as shown in the following : 

TABLE III 

CJOREtELATION BETWEEN STAND AND YiELD 
Cutting iBt 2d M 

Correlation + .78 ± .04 + .55 ± .07 + .47 ± .08 

Cutting 4th 6th 6th 

Correlation + .54 ± .07 + .10 ± .10 + .70 ± .05. 

The exceptionally low coefficient of the fifth cutting was 
due to the low yields on the part of plots which had good 
stands but were relatively inactive during the hot 
weather and partial water famine which occurred at this 
period. On the other hand, certain plots through their 
resistance to heat and consequent activity at this period, 
overcame to a large extent their handicap of poor stands, 
and nearly obliterated the usual plus correlation between 
stand and yield. 

The data thus studied en masse indicate at least two 
physiological groups which are unequally sensitive to the 
climatic changes which occur in the course of a growing 
season, and whose reactions were sufficiently strong to 
change almost completely the order of the productivity of 
the {dots. In order to test this conclusion let us turn to 
the individual plots and endeavor to discover and classify 
the physiological varieties indicated above. 

If, now, we arrange the forty-four regional strains 
according to their morphological characters and geo- 
graphical origin, we shall have five more or less distinct 
groups as follows: Mediterranean, Peruvian, European, 
American and Turkestan. The behavior of these varietal 
groups through the course of six cuttings during the sum- 
mer of 1910 substantiates the conclusions already drawn 
and illustrates the sharp differences in climatic reactions 
which may be observed in the several varieties of a single 
species. 



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No. 570] ALFALFA BREEDING 361 

Morphologically the Mediterranean and Peruvian al- 
falfas are so distinct in type that any one at all familiar 
with the different kinds of alfalfa would recognize them 
at a glance, whether a whole field or a single plant be 
observed. The presence of yellow or greenish blue flow- 
ers also determines a variety to be of northern origin with 
mixtures of falcata characters, which usually carry with 
them resistance to cold and drought. Otherwise, the 
Turkestan, American and European types are so nearly 
alike that only an expert would recognize them in mass 
culture. The individual variations within these three 
types intergrade to such a degree that one could scarcely 
assume to judge, from the observation of a single plant, 
the type prevailing in the field from which it originated. 
The three types, however, differ markedly in their phys- 
iological reactions as we shall presently see. The distinc- 
tions, in this regard, as exhibited on our plots, are not 
nearly so marked between the American and Turkestan 
alfalfas as between these two types, on the one hand, and 
the European, on the other. However, in northern cli- 
mates where winter resistance enters as a i)otent factor, 
the Turkestan alfalfa exhibits greater hardiness than the 
American form, and, therefore, is able to maintain a more 
perfect stand through seasons of extreme frost. 

When grown under Arizona conditions, the average 
yields of each of these five type groups present seasonal 
curves at once striking in their diversity and contrasts. 
These differences are exhibited more easily by plotting 
the average of all the plots as a straight line, and the aver- 
age of the different groups as percentages of the total 
average above and below the general average line. 

In observing Fig.l, we are first impressed with a marked 
similarity in the performance of the European and Medi- 
terranean alfalfas, on the one hand, and the American and 
Turkestan on the other, and also with the striking differ- 
ences exhibited between the two groups. Although the 
average yield of the European plots greatly exceed that of 
the Mediterranean plots, the shapes of their respective 



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362 



THE AMEBIC AN NATURALIST [VoL-XLVDI 



curves are almost exactly alike, tlie greatest relative yield 
of each being in the heated part of the summer after the 
beginning of the water famine. In like manner, the 
American and Turkestan varieties made similar relative 
yield curves, that for the Turkestan being slightly above 
the curve for the American strains. Here, however, the 



CUTTING 

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a. 31. 

31 
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12 

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f 



AVE. YIELD 3 f i'J'LBa. 



1^ 
U 
It 

2L 




Sf^iM 



Relati\'g Yield of Regional Vabieties Based on tub AvEBAaB of All Plots 

AS 100 Pbb Cent. 

curves bend strongly downward in mid and late summer, 
as if these types were much less resistant to the accumula- 
tive effects of drought and heat. In fact, it would seem 
that during the hot period included within the fifth cutting 



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No. 670] ALFALFA BREEDING 363 

(July and August), the American and Turkestan varieties 
were comparatively inactive, yielding only about eight 
hundred pounds of dry hay per acre, as against more than 
1 ton and a half each on the first cutting. The relative 
ield curve for the Peruvian type stands separate and dis- 
tinct from the others. Although here, as with other varie- 
ties, the yield declines with the advance of the season, the 
persistence and vigor with which this strain resisted the 
summer heat and drought caused it to gain rapidly on the 
other varieties in relative yield throughout the season 
until the very last cutting, when there was a slight decline. 

Disregarding the shape of the curves we may now notice 
the total yield for the season. In this respect the different 
regional varieties take the following relative order: Peru- 
vian, European, Turkestan, American and Mediterranean. 
It is here noticeable that, though the European and Medi- 
terranean varieties have similar seasonal yield curves, 
they are not contiguous in the arrangement based on total 
yields. This is a result of a marked difference in the 
stand maintained by the two varieties which averaged 
ninety-two per cent, for the former and seventy-four per 
cent, for the latter. In their ability to maintain stand, the 
Peruvian, European, Turkestan and American varieties 
were about equal, averaging 92, 92, 93 and 94 per cent., re- 
spectively. The lack of stand on the part of the Medi- 
terranean alfalfas was not due to the poor quality of the 
original seed, for all of these plots once had perfect stands. 
This behavior is also in accordance with the records of 
other fields of Mediterranean alfalfa in the southwest, 
which have come under the observation of the writer. The 
explanation of the weakness of the Mediterranean and 
corresponding strength of the otherwise similarly reacting 
European alfalfa in maintaining stand under Arizona con- 
ditions is a subject for further careful physiological study. 

The recognition, analysis, and calibration of these dif- 
ferences of the physiological reactions of varieties are 
thus seen to become a first essential in the study of cli- 
matic adaptation^ and form the basis for rational pro- 
cedure in the choice of varieties and in selective breeding 
for the improvement of the same. 



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364 THE AMERICAN NATURALIST [Vol. XLVIII 

Correlations 
In the improvement of varieties of plants, quality is 
often as important as quantity of yield. This is especially 
true in a forage crop, such as alfalfa. Since nitrogen, next 
to fat, is the most expensive of the necessary food constit- 
uents, it may be taken as the measure of quality. Com- 
merical buyers judge alfalfa hay by its purity, odor, color 
and percentage of leaves retained in curing and baling. 
The value of the leaves lies in their relatively high nitro- 
gen content and the consequent increased food value which 
they impart to the hay. Expressed quantitatively, the cor- 
relations between the nitrogen content of the hay and the 
percentage of leaves for the six cuttings were as follows : 

TABLE IV 

CfOEBELATION BETWEEN NITROGEN CONTENT OP HaY AND PEB CENT. OP LEAVES 

Cutting Iflt 2d 3d 

Correlation + .46 ± .08 + .61 ± .06 + .72 ± .05 

Cutting 4th 5th 6th 

Correlation + .68 ± .05 + .61 ± .06 + .52 ± .07. 

That the final value of the hay is markedly dependent upon 
the composition as well as the percentage of leaves is 
shown by the following high and fairly uniform correla- 
tion between the nitrogen content of the hay and the nitro- 
gen content of the leaves : 

TABLE V 

Correlation between Nitrogen Content op Hay and Nitrogen Content 

OP Leaves 

Cutting Ist 2d 3d 

Correlation + .69 ± .05 + .73 ± .05 + .42 ± .08 

CuttliiR 4th 5th 6th 

Correlation + .67 ± .06 + .85 ± .03 + .74 dt .05. 

If, now, we have shown that the quality of the hay de- 
pends primarily upon the percentage and composition of 
the leaves, we may proceed to investigate those factors 
which indirectly modify the feeding value by influencing 
the amount or character of these organs. 

The factors most profoundly affecting the percentage 
of leaves were yield, height and stage of maturity at 
which the cutting was made. Local or varietal forces were 



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No. 570] ALFALFA BREEDING 365 

suflBciently constant to hold the place variation of this 
character to the plus side of the equation for four out of 
five determinations made, as is seen in the following 
table: 

TABLE VI 

Place Variation in Pbbcentagi of Leaves 

Cutting 1 and 2 2 and 8 8 and 4 4 and 5 5 and 6 

Correlation. + 10 ± .10 + .23 ± .10 + .16 ± .10 + .46 ± .08 — .12 d: .10. 

These correlations, however, are low and seem to indicate 
that tihie natural varietal traits were being overcome and 
obscured by other variable factors. 

Contrary to expectation, the stand had little to do with 
the percentage of leaves, as the following low and incon- 
stant correlations show. 

TABLE VII 

COREELATION BETWEEN THE PERCENTAGE OF LEAVES AND STAND 

CnUinK 1st 2d 3d 

Correlation — .14 ± .10 — .02 ± .10 + .03 ± .10 

CatUng . 4th 5tb 6th 

Correlation + .10 ± .10 + .07 ± .10 + .24 ± .10. 

On the other hand, the relation between height and 
yield and percentage of leaves was constant and marked, 
except in the last two cuttings. 

TABLE vin 

COBKELATION BETWEEN PERCENTAGE OP LEAVES AND HEIGHT AND YiELD 

Catting l8t 2d 8d 

Yield — .41 ± .08 — .60 ± .07 — .15 ± .10 

Height — .48 ± .08 — .62 ± .06 — .68 ± .05 

Catting 4th 5th 6th 

Yield —.40 ±.09 + .20 ± .10 + .30 ± .09. 

Height — .55 ± .07 + .09 ± .10 + .19 ± .10. 

The sudden change from minus to plus in these correla- 
tions should be noted. The average heights of the first 
four cuttings were 32, 30, 28 and 27 inches, respectively. 
The average height of the fifth and sixth, were 15 and 12 
inches. This would suggest that at or below 15 inches the 
mutual shading of the stems is not suflBcient to cause an 
appreciable shedding of the lower leaves. Up to this 
I)oint, moreover, growth usually takes place by an increase 



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366 THE AMEBIC AN NATURALIST [Vol. XLVIH 

in the number of nodes, each with its accompanying leaves 
and side branches. Above fifteen inches, however, the 
principal growth in height consists in a lengthening of the 
intemodes and, consequently, a relatively greater produc- 
tion of stem as compared with leaf tissue. In this phys- 
iological correlation lies the core of the difficulty in breed- 
ing at once for quality and quantity. The act of high pro- 
duction within itself cuts down the quality of the product 
by reducing the ratio between the leaves and the stems. 

This difficulty, moreover, occurs in the composition as 
well as the percentage of the leaves. The correlation ex- 
isting between the nitrogen content of the leaves and the 
number of days required to mature a cutting is shown in 
the following table : 







TABLE IX 


COEBELATION 


BETWEEN 


THE Nitrogen Content of Hay and the Period 
Eequtred roR Maturity 


Cutting 

Correlation . 




l8t 2d 3cl 
... —.33 ±.09 —.30 ±.09 —.27 ±.09 


Cutting 
Correlation. 




4th 5tb 6th 
... —.52 ±.07 —.50 ±.08 —.17 ±.10. 



Quickly maturing varieties thus have leaves richer in 
nitrogen than those which require a greater length of time 
for completion of growth. When, however, we take the 
average number of days required throughout the season 
to mature a cutting for each plot and compare this with 
the total seasonal yield we find a correlation of + .43. 
Thus we are again confronted by a minus correlation be- 
tween quality and yield which must be overcome if we 
would make progress simultaneously in both lines. 

As further examples of antagonistic correlations, a few 
instances may be taken from the data furnished by forty- 
three plots of pure races of alfalfa grown during the sum- 
mer of 1910. The correlation between height and percent- 
age of leaves was again constant and marked. The results 
here paralleled those found for the regional varieties. 
Whereas yield was uniformly correlated i)ositively with 
both stooling capacity (av. No. stems per plant) and 
height, it is interesting to note that there was also a uni- 



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No. 570] 



ALFALFA BREEDING 
TABLE X 

CORBBLATION IN PUBE BaCIS 



367 



Correlation Between 


Cuttiogs 


July 


AugUBt 


September October 


Green weight and average 
number stems 

Green weight and average 
height 


+ .76 ±: .04 
-h .01 d= .10 

— .29 =b .09 

— .39 ± .09 


4- .42 rb .08 
4- .44 ±.08 

— .19 ±.10 

— .15 ±.10 


4- .62 ± .06;+ .50 ± .08 
4- .22 ± .10 4- .33 ± .09 


Average height and number of 
stems 


- .32 ± .091— .21 ± .10 


Average height and per cent, 
leaves 


— .55 ± .07 -- .51 ± .08 



form minus correlation existing between them. We thus 
have two factors both making for yield, but seemingly 
(probably physiologically) aatagonistic to each other. In 
breeding for high yielding strains we are here again called 
upon to overcome by selection an antagonistic physiolo- 
gical correlation. 

This brings us to the following final conclusion which 
the writer wishes to emphasize : 

In economic plant breeding one frequently encou/nters 
physiologically negative correlations such as those, in 
alfalfa, between height and stooling capacity, height and 
percentage of leaves, and between yield and quality. In 
seeking improvement, therefore, the breeder must recog- 
nize and make use of these facts in the interpretation of 
results obtained, and also search for races which violate 
su^h naturally antagonistic correlations to the greatest 
possible extent. 

Geisteral Conclusions 

That the complex of allelomorphs, which we call a va- 
riety, may be definite as both to ultimate composition and 
organization is not here questioned. When, however, we 
consider that visible characters are only the expression of 
the reactions of the vital forces of the plant with the en- 
vironment, we can realize that the variety, as we see it, is 
not a definite thing, but is a result of two independent 
classes of factors. Change either and the result corre- 
spondingly changes. 



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368 THE AMEBIC AN NATURALIST [V0L.XLVIII 

We are therefore to look upon the variety as a delicately 
organized chemical compound. The various factors of 
climate and soil may be compared to different physical 
influences to which the original compound may be sub- 
jected. As the chemist would expect reactions varying in 
accordance with the physical stimuli used, so will the plant 
react in agreement with the different environmental com- 
binations. The extent to which this will change the nature 
and appearance of plants is often far reaching. Cook, 
working with cotton, has found that certain cultural condi- 
tions at an early stage of growth will make profound dif- 
ferences in the method of branching which determines the 
whole subsequent development of the plant and affects 
materially its economic value. Cultural and climatic reac- 
tions often lead to error among those who assume them to 
be mutative changes induced by the new conditions. That 
these reactions may bring to light sub-races with heredi- 
tary tendencies not hitherto called into expression and 
which, by selection, may be secured as pure races, is the 
probable explanation of many cases of supposed direct 
climatic adaptation. 

Thus, realizing the true nature of a variety, we can 
draw further upon the analogy of the chemist who investi- 
gates an imknown substance by testing its reactions with 
a large number of known reagents. In like manner the 
breeder can only understand the true nature of the hered- 
itary vital forces within a plant after he has tested and 
calibrated its reactions against a variety of soil and cli- 
matic factors. These reactions are of interest to the 
farmer only in so far as they affect the economic value of 
the variety as grown in his own locality but to the breeder 
and student of heredity their importance is fundamental. 
This is so because they enable him to classify, coordinate 
and interpret the experimental results that he obtains. 
This ability finally must form the basis of all rational pro- 
cedure, whether one be engaged in the study of pure gen- 
etics or in the operations of practical plant improvement. 



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TAXONOMY AND EVOLUTION 

ByX 

'' Some passages in this book, if taken alone and read hastily, may 
appear to discourage systematic Zoology. This is far from my inten- 
tion. No one can study the great naturalists of the seventeenth and 
eighteenth centuries without feeling how seriously their work is impaired 
by the defective systems of the time. It is not systematic but aimless 
work that I deprecate — ^work that springs from no real curiosity in 
Nature and attempts to answer no scientific questions." — L. C. Miall, 
" Natural History of Aquatic Insects," Preface, p. L 

i 

Introduction 

LiNN^us bestowing Latin names upon animals and plants 
was simply tripping gaily across the back of a half submerged 
Behemoth and mistaking it for dry land. Now the beast is 
careering around, and in spite of zoological congresses and inter- 
national rules nobody quite knows what to do with him. No 
doubt when some zoological czar arises and issues his fiat a uni- 
form system of nomenclature will be adopted and things will 
begin to straighten themselves out. This can only be a matter 
of time — ^the past can not be altered. On systematists to-day 
necessarily devolves the dull, diflBcult and important duty of 
going through the descriptive work of the early naturalists and 
emending it; so that Spallanzani's derisive sobriquet of 
** nomenclature naturalists'' was a little unjust, even in his time. 

Whatever opinions may be held upon the genius of Linnaeus, 
in justice to him it should be said that it was not until his ex- 
ample had been followed by a crowd of other workers eager to 
attain to immortality by way of the back door he had left open 
that the fat was really in the fire. 

Well knowing the confusion into which systematic work in 
zoology was brought by the early naturalists, modem systemat- 
ists in our opinion will be the authors of a similar confusion in 
the future if some of the slipshod methods of modem syste- 
matics are not corrected. Moreover, a confused nomenclature 
is not the least of the evils which second-rate systematic work 
brings in its train. 

369 



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370 THE AMEBIC AN NATURALIST [V0L.XLVIU 

Systematisfts with a proud curl of tbe lip may tell us that the 
work is not done now as it once was. Indeed, to those who are 
not able to project themselves into the future it may seem in- 
credible that the systematists of a later date will be able to find 
much room for complaint in the elaborate descriptions and care- 
ful figures of modem descriptive writers. For the moment, how- 
ever, it €niffices us to point the parable by remarking that in 
1780 Spallanzani was able to refer to the '* beautiful figures'' 
and ** careful descriptions" of a systematic worker on frogs. 
We, of course, know without seeing them that the figures were 
not beautiful nor the description, careful — any way in the sense 
of being complete. We have therefore to reflect whether the 
zoologists of a future generation will find the work of to-day any 
freer of faults than that of the past centuries. 

Systematic Work. General CoNsroERATioNs 

It is necessary to insist at once that systematic work is not 
merely a question of nomenclature, names and novelties. Sys- 
tematists have only themselves to thank if such a narrow con- 
ception of their province is very widely spread, especially 
among morphologists and anatomists, who are ready to belittle 
the value of the systematists' work. But science is measurement 
and zoology — if you like — is description, and it is impossible to 
dispense with the ^stematists' descriptive work. But we think 
it possible to dispense with a good deal of stuff after this 
fashion : 

Metopidium high, suprahumerals rather long, acute, arcuate and 
curved at the tips. Pronotum roughly punctured at the. bottom of fine 
furrows. Color dark-ochreous. Posterior horn uniformly cylindrieal, 
undulating or sinuous without rugosities. Underside, scutellum and 
legs sordid-ochreous. 

The phrase ''sordid ochreous " comes ready to hand and 
makes it unnecessary for us to go in search of a suitable com- 
ment. 

**This is the 30th memoir" writes a systematist "on the 
Zonitidae which I have published in this journal, describing in 
all about 560 new species." We feel inclined to put our hands 
resolutely on his shoulders and inquire if he ever saw a cteno- 
phor swimming in the sea or watched the progress of an Asierias 
towards its prey. 



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No. 570] TAXONOMY AND EVOLUTION. 371 

No one can look unmoved upon the Hymenopteran or Helicoid 
specialist with head bent over a drawer full of shells or dried 
insects on pins. It is not that we resent concentration or enthu- 
siasm or even specialization, but the systematist has lost touch 
with his own science of zoology. 

Zoology, a cornucopia of marvels, lies at his elbow full to over- 
flowing, but he is unmindful of it. It is as if a man should use 
the Parthenon only as a convenient place on which to strike a 
match for his pipe. 

The divorce between systematic work and the rest of zoology 
is the more regrettable because it is practically complete. It is, 
we admit, expedient that zoology should be divided up into 
anatomy, morphology and so on. But such a division is allow- 
able only when it is expedient, while for intellectual purposes 
such a division is and has always been a danger. To obtain 
facts one must be an analyst, to consider them one must be a 
j^ynihesist. Between the two there is all the difference between 
a hodman and a natural philosopher. 

But our contention is that not even the plea of practical ex- 
pediency can justify the extreme state of specialization into 
which systematic zoology has fallen, making itself manifeeft in 
the concatenation of such purely artificial characters as that 
*'the third joint of the antenna is longer than the second, that 
the mesoscutellum is ovate and the color pink with blue spots.'* 
All this simply makes one yawn, though there is this much to be 
said in favor of this stamp of systematist, that nothing bores 
him so much as the recitation of one of his own diagnoses or 
being introduced to the systematist of another group. 

Systematic work is a withered branch of the biological tree 
which there is still hope of rejuvenating. Treviranus long ago 
remarked that if we once regarded systematic work as a part of 
biology and nomenclature as a means to an end rather than as 
an end in itself, both might take their places in science. Let us 
take every precaution against systematic work becoming one of 
those unproductive and artificial pursuits which spring up like 
mushrooms around centers of splendid endeavor and high 
achievement. After Shakespeare came his commentators. Shall 
it be said that after biology came the systematists t 

We assume that the principal object of systematic work is to 
discover the phylo-genetic classification of animals, for which it 
is surely necessary that every animal as it passes through the 



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372 THE AMERICAN NATURALIST [Vol.XLVIII 

systematists' hands should be, as far as possible, thoroughly ex- 
amined and described, no dependence being placed upon a few 
superficial characters usually selected from the external parts t 
That the systematist should concern himself, as he does, with 
the external parts, leaving the anatomy to other workers, we 
consider is as bad for the systematist himself as it is bad for the 
science; for himself, he is doing work which can only keep his 
soul alive with diflBculty — superficial clerical work which can be 
"prompted by no real curiosity and attempts to answer no 
scientific questions," and the results of the work itself is often 
invalidated by the arrival of the destroying angel in the person 
of the anatomist. For a superficial description often means a 
wrong classification ; whence it follows that any zoo-geographical 
deductions therefrom are invalidated; while a careless descrip- 
tion usually ignores the possibilities of variation and shows no 
evidence of pains having been taken to make identification easy. 

Systematic work, then, is concerned with classification, geo- 
graphical distribution, variation and identification, and there 
would be no need for this paper, if it were more generally re- 
alized that one thorough examination and description of the 
whole animal assists those branches of the inquiry more than 
twenty loose and superficial ones. 

Of course systematic workers are not the only zoologists who 
over-publish; yet they especially might cultivate a little of the 
salutary reticence of C. L. Nitsch and Alfred Newton, who, with 
no discredit to themselves, wrote and published little, yet it must 
be admitted by those with an eye on the extravagant output of 
others, to the advantage of zoology. The words "res non-verba*' 
were the motto of Delle Chiaje, who, like Nitzsch, on his death 
left behind many important discoveries unpublished and only 
indicated in his drawings. 

Classification in Genera i. 

The coming of Evolution meant for systematic workers that 
no system of classification would henceforth be considered as a 
serious contribution to science, which was not constructed on 
phylogenetic lines. It meant the final overthrow of such ideas 
as Agassiz held, that the divisions of the animal kingdom were 
instituted by the Divine Intelligence as categories of his mode of 
thought — of such fantastic systems as those of Bafinesque and 
Swainson and such strictly artificial ones as the arbitrary ar- 



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No. 570] TAXONOMY AND EVOLUTION. 373 

rangements of convenience which should be now used only in 
those groups where, and for as long as, our knowledge of the 
anatomy is so slight that some sort of temporary device for 
sorting out genera and species has to be adopted. 

The ideal system is now phylogenetic, i. c, it aims at recon- 
structing in a genealogical tree the actual lines of descent. 

Only those who have attempted the reconstruction of phylo- 
genetic trees understand the intrinsic difSculties of the work. 
There can be no doubt that the coming of Evolution has put 
before the systematist a very difficult task. As to whether the 
methods usually employed by him are adequate to the demands 
placed upon them we are frankly sceptical. 

Fortunately for the systematist the main lines of classifica- 
tion in most groups are given him ready made by the morphol- 
ogists who have laid down the foundations trusting to the ''s3n9- 
tematist" to fill in the details. Such classifications — ^the main 
phyla, classes and orders are of permanent value, because they 
are founded upon a combination of characters of tried worth 
judiciously selected after a careful survey of extensive embry- 
ological and anatomical data. 

Single Character Classification 

On the other hand the minor systems — ^the families, genera 
and species — the realm of the ''systematist*' — too frequently 
consist of haphazard combination of a few character selected 
because of their convenience in not entailing any anatomical 
work, or selected on account of the ignorance existing of any 
other — particularly internal — important characters. Ignorance 
of their morphology has been the main reason for the difficulty 
in classifying the Coleoptera. Entomologists are especially 
prone to give their whole attention to what is visible without 
the aid of dissection. In the Polyzoa the majority of forms are 
only known by their external appearance and their classification 
is proportionally unsatisfactory. In the MoUusca reliance is 
placed on the shell ; in mammals the skull and the skin, in birds 
the plumage are the articles of faith. 

Single character classification or diagnosis by one or two 
characters, as zoological history shows, has proved inadequate — 
that it is unphilosophical is patent to all. 

Such single character classification even when practised by 



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374 THE AMEBIC AN NATURALIST [VoL.XLVIII 

the great morphologists, men who, being acquainted with the 
whole of the anatomy of the forms they were classifying, de- 
liberately selected one or two characters after a survey of the 
whole — was rarely a success. Huxley set out unabashed to 
classify birds by their palate, and Agassiz fish by their scales — 
^stems which have now shared the fate of most others which 
set out to erect a classification on the modifications of a single 
organ alone. Alfred Newton said that there was no part of a 
bird's organization that by a proper study would not help to 
settle the great question of its aflBnities. 

The systematist who deals with the minor subdivisions of the 
animal kingdom — families and genera — should be as much a 
morphologist as the one who deals with the larger — the phyla 
and classes. 

Description 

We have pointed out above that the adequacy of a system of 
classification depends in great measure upon the thoroughness 
of the description of the species and genera. Classification in 
all groups has progressed in just proportion to the more exact 
examination of the species considered in the classification. 

The history of zoological research brings out this fact very 
clearly, beginning with the work of Linnaeus, the originator of 
the superficial diagnosis, passing on through Cuvier, who appre- 
ciated the value of anatomical knowledge, to Von Baer, wbo 
emphasized the importance of embryology. 

It was not a "systematist" as we know him who first correctly 
classified Lepas — ^the conchologists blindly accepted it as a 
Mollusc. It was not a ''systematise' who first established Peri- 
patus as an Arthropod, for the first describer of that animal 
regarded it as a slug I 

How rare it is to find in a description of a new species any- 
thing more than an indication of the external parts. It is a 
peculiarly arbitrary limit to a man's curiosity that restricts 
his enquiry to the superficial aspect of an animal. A natural 
philosopher ought never to be satisfied with the external ap- 
pearance of things. The wisdom of the ancients bids us ** be- 
ware of what things appear "; and the method of our modem 
science is one of close and detailed observations. In scattering 
names broadcast with liberal largesse upon species, varieties and 



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No. 570] TAXONOMY AND EVOLUTION. 376 

genera, (systematists have sometimes dropped into some carions 
errors. Teratological specimens have been described as new 
species and most zoologists have heard of the man who de- 
scribed as a new species the longicom beetle, the head of which 
having fallen off, had been fixed on upside down. His examina- 
tion of a new species makes so slight an impression on his mind 
that sometimes the same worker has described the same form 
twice under different names. 

The descriptive papers on Mollusca usually consist of short 
descriptions of the shells, even written in a dead language. This 
is conchology. Conchologists confine themselves to the pat- 
terns and shapes of shells — ^nature's medallions — numismatics I 
Much of this work — along with similar productions in entomol- 
(^y and carcinology — we regard as positively flagitious. 

Sir Ray Lankester in the article ** Zoology" in the Encyclo- 
paedia Britannica (ed. XI.) remarks that museum naturalists 
must give attention to the inside as well as to the outside of 
animals and that to-day no one considers a study of an animal's 
form of any value which does not include internal structure, 
histology and embryology in its scope. Agassiz, too in his 
famous ** Essay on classification" wrote that ''the mere indi- 
cation of a species is a poor addition to our knowledge when 
compared with such monographs as Lyonnet's Cossus, Bojanus' 
'Turtle' Strauss Durckheim's Melolontha and Owen's Nauti- 

**But," it will immediately be asked in chorus, *'do you 
seriously suggest that a monographic volume should be devoted 
to every new species!" 

This is a leading question which brings us to the crux of the 
whole matter, and can not be answered in simple '*Yea" or 
**Nay." 

The Provisionali Diagnosis 

The amount of analytical study that may be given to «iny one 
animal form in any one stage of its development is infinite. 
The result is that in describing a new species for the purposes 
of exact phylogenetic classification there must be a limit beyond 
which it is unnecessary to go. Such a limit can not be otherwise 
than arbitrarily selected according to the best judgment of the 
fi^rstematic worker as to how much analysis is required to pl€u^ 
his new species, although at present, miserabile dictu, relatively 



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376 THE AMEBIC AN NATURALIST [VoL.XLVni 

very few animals have been thoroughly explored, yet in the dis- 
tant future, in the millennium, it can not be doubted that every 
genus, even every species will have been examined in toio in every 
stage of its development and life-history as thoroughly as our 
instruments and eyesight will allow, and perhaps a whole vol- 
ume or several volumes will be devoted to every animal form. 
At present, however, it is a waste of ink to consider a future so 
far away. A more pressing duty is to consider how far modem 
methods of superficial diagnosis fulfil the obligations placed 
upon systematists not to give an exhaustive analysis of animal 
forms, but to give suflScient data to meet the searching demands 
of phylogenetic classification. 

"We are aware of the fact that the convinced and determined 
systematist does not maintain that the method of superficial 
diagnosis does meet or is intended to meet the demands we have 
been indicating. If he reads as far as this and does not throw 
aside this paper in contempt, he is ready with eager forefinger 
and glib apology to convict us of begging the question that sys- 
tematic zoology can be ever anything, or should be ever any- 
thing more than we have said. 

It is often argued that the superficial diagnosis of the syste- 
matic worker is simply a provisional diagnosis awaiting the con- 
firmation of the anatomist. A plausible defence of the provi- 
sional diagnosis is advanced by many workers in perfect good 
faith which it is now necessary to anticipate and examine. 

This argument defends the provisional diagnosis on two 
grounds: (1) The advertisement theory; (2) the recognition 
mark theory. 

The supporters of these theories admit that the provisional 
diagnosis in no way settles either an animal's systematic posi- 
tion or its validity as a species. But it is alleged to be of value 
and should be encouraged because it advertises the existence of 
a presumptive new form which would otherwise renmin un- 
known and overlooked in the store rooms of the museum and 
laboratory, and because in giving an account of the external 
parts, at all events, the systematist is describing those features 
by which we are more or less easily able by a superficial exami- 
nation to recognize summarily the form when it turns up again. 

The first part of our answer amounts to a recapitulation of what 
has been previously stated in general, viz., that systematics have 
lost touch with the rest of the science. The output of systematic 



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No. 570] TAXONOMY AND EVOLUTION. 377 

work and the output of aiiat<Mnical and morphological work 
nowadays move along completely different channels. The work 
turned out by the systematic worker is scarcely, if ever, con- 
ceived in the light of modem biological theory, is rarely couched 
in terms of modem biology and rarely indicates a problem to be 
solved or a question to be answered. It proposes distinctions 
the anatomist sweeps away and hazards affinities the morphol- 
ogist laughs at. It performs work that has to be done over 
again, and instead of giving the morphologist what it claims to 
give him — a sketch map of the country he is to traverse — cdl it 
does is to bewilder him with a Will-of-the-Wisp's lantern, an 
intolerable multitude of slipshod and untrustworthy directions 
that he has come instinctively to suspect. We can not too often 
ask the question, why should the work be done twice! Surely 
it is time that something were done to stop this tremendous rush 
for publishing provisional diagnoses that more time could be 
devoted to the systematic study of animal forms, obtaining 
thereby sound phylogenetic classification, sound deductions in 
geographical distribution, valid species and a less confused 
nomenclature. 

Thus the systematist's protest that at least he ** advertises" pre- 
sumptive new forms we can reply that he may do so, but that for 
any purpose other than a dull census of the animal kingdom with 
a very generous '*±" to it, he is a positive Benedick of zoolo- 
gists, for ** nobody marks him.'' 

The upholders of the provisional diagnosis will say that at 
any rate they are giving us a description of the external parts 
and are increasing our knowledge by so much. True, but by so 
inconsiderable an amount that when the anatomist comes along 
with his scalpel he so quickly disposes of the external parts 
merely by the use of his eyes that it is a matter of indifference 
whether the former have been described or not. Moreover, the 
great majority of the tens of thousands of descriptions that are 
issuing from the press are of animals so closely related to pre- 
viously described species that such descriptions really amount 
to little more than a recitation of their distinguishing characters. 

It is certainly useful to know that Caccabis rufa is to be dis- 
tinguished from Perdix cinerea by its red legs and that the 
LeporidaB can be discriminated by the character of their upper 
incisors. But the question may well be asked, what is the use 
of being able to distinguish one species from another without 



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378 THE AMERICAN NATURALIST [Vol. XLVIII 

being able to record at the same time anything about its bionom- 
ics or anatomy which would give the distinction its real value. 
A great deal is known about the partridges and hares, hence the 
distinctions alluded to above are useful as an easy way of 
quickly identifying them. But so long as nothing is known 
about either of two species that are distinguished we are none 
the worse oflP, if both remain indistinguishable. 

Finally we would point out that of all people the systematist 
should know that at present of the forms he advertises and 
describes so copiously and summarily only a fractional part is, 
or can be, dealt with by the laboratory worker. We are speaking 
now of the anatomy pure and simple of new species and genera. 
The laboratory worker proceeds slowly, is fewer in numbers 
and has other problems — embryology (descriptive and experi- 
mental), heredity, physiology (descriptive and experimental) 
and morphology to attend to besides purely descriptive anatomy. 
And yet anatomy — ^the very corner stone of the temple of 
zoology — ^has to be restricted in output because none of the sys- 
tematists will learn how to use a scalpel or look down a dissect- 
ing-microscope — feats in themselves perfectly easy and calling 
for no special training or faculties. 

Possibly the upholders of the provisional diagnosis will main- 
tain that by publishing his account of the difference between 
closely allied forms the systematist is providing the biologist 
with a stimulus to discover how much deeper such differences go. 
But surely it is a strange perversion of a man's natural instinct 
of curiosity that enables the systematist to rest content with 
advertising problems instead of endeavoring to equip himself 
for the task of undertaking them himself, who is eminently 
suited to the work and whose occupation daily brings him into 
close contact with them. 

Finally we would point out that the enormous mass of species 
which have been created upon superficial diagnosis so far have 
remained unincorporated for the most part in the structure 
it is designed to build up, viz., a clear comprehension of the 
phylogeny of the lesser divisions of the animal kingdom. It is as 
though a man were to set about building a house by making a 
vast quantity of bad bricks and then to leave them scattered 
about his site in the hopes that some one would come along and 
make a house of them. Surely it is an economy of effort for the 
systematist to take up the bricks and build himself, what time 



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No. 570] TAXONOMY AND EVOLUTION, 379 

the embryologist and morphologist are engaged upon their own 
special tasks. 

The Compabattve Value of Internal and External Parts 

Briefly reviewing the discussion as far as we have carried it, 
it will be seen that we are asking for sound phylogenetic classi- 
fication of the smaller groups as well as of the larger ones, based 
not upon single characters, but upon the whole of the characters 
regarded collectively, for more careful and more thorough mor- 
phological methods in description and for the discontinuation 
of the provisional diagnosis. In view of the desirability of work- 
ing up sounder schemes of classification from the enormous, un- 
wieldy and superficially known mass of genera and species sys- 
tematists can be rendering little service by continuing to turn 
out indiscriminate provisional diagnoses. 

It remains now to discuss in greater detail the proposal we 
bring forward in the place of the provisional diagnosis. 

The commonly accepted opinion is that while for the classifi- 
cation of families and orders the internal parts must be taken 
into consideration, for that of species and genera a summary of 
the external parts is all that is required. On account of the 
labor and diflSculty sometimes involved in dissection we are too 
ready to assume that the internal parts in genera and species 
present a dismal monotomy of character which it would be 
profitless to investigate for systematic purposes. 

If it is admitted that internal characters are of value among 
the higher divisions of the animal kingdom, can the systematist 
tell us at what precise point in the downward scale they cease to 
have value, and at which reference need only be made to the 
external parts? Even supposing for a moment that there is 
such a limit, we are strongly of opinion that it does not come 
before the genera. 

A genus is of different value in different groups but as a rule 
it presents so much difference in external form from other 
genera as to warrant the inference that internal differences of a 
like extent will be found if sought for. At the present moment 
a genus is a perfectly arbitrary collection of species. We ven- 
ture to prophesy that with more elaborate descriptions inter- 
generic relationships will be more carefully defined and genera 
will become less heterogeneous and more natural. But this is 
by the way. 



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380 THE AMERICAN NATURALIST [VoL.XLVHI 

A priori it seems improbable that less variety will be found 
among the various internal systems of organs than in the in- 
tegumentary or exoskeletal parts. But an argument may be 
put forward that the external parts in immediate contact with 
the environmental forces would be the first to register change in 
the modification of a species. The internal parts as stanchions 
and bulwarks remain firm to give characters to orders and fami- 
lies, while change makes assault without and gives characters 
for species. For example, among the Asteroids it is said that 
the internal organization is so uniform that the only method of 
classification is to take the different ways in which the demands 
of the external environment have been met. 

But generally speaking a species depends for its survival not 
simply upon the external front it presents to its environment. 
An animal's form cannot arbitrarily be divided into external 
and internal parts. It is an integral whole, and variation and 
selection may occur anywhere, while the correlation of variation 
is a text-book commonplace. As opposed to correlative variation 
there is the law of the independent variation of parts. Not only 
may variation occurring in one part cause a variation to take 
place in another, but variation may take place independently in 
some areas and be limited in another, so that in deciding upon 
the comparative value of the internal and external parts in any 
group consideration must be given to both these laws. In the 
Asteroids, we assume that anatomists have taken the matter in 
hand and found that the external parts vary as a rule independ- 
ently of the internal which remain constant. But in how few 
groups has such a precaution been taken I Is it not rather the 
general rule simply to assume that the internal parts lack varia- 
tion and are of no value systematically, as, for instance, in the 
Lepidoptera, where the Lepidopterists expect that a classification 
based upon the wing-markings or upon wing-neuration can ex- 
press the true relationship of the various units! 

Even in those groups where systematists have dissected and 
found the internal parts valueless it still remains necessary, in 
view of the law of independent and unexpected variation of 
parts for them, to apply the scalpel to every new form. 

It is impossible to deny that the external parts are often of 
extreme systematic importance — ^they are exposed to the light 
and develop color patterns (although color is usually an unsafe 
guide if taken alone), and the external parts of such forms as 



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No. 570] TAXONOMY AND EVOLUTION, 381 

Arthropods and Molluscs being hard provide syptematists with 
a sculpture on which it is easy to detect minute diflferences in 
pattern. On the other hand we would remind the conchologist 
that the external parts are by their very positions most liable 
to exhibit lesions and weathering, and certainly in the case of 
Mollusca where the dependence of the exoskeleton upon a spe- 
cific article of diet (viz., lime salts) is very close, to register 
** fluctuating variation" according to the constitution of the 
medium or of the food ingested. 

But here again if a more common practise were made in dis* 
secting by systematists, variations would be found even in closely 
allied species making the descriptions complete and often 
even necessitating the erection of new genera. One of the 
writers was dissecting an ordinary species when he discovered 
that the epipharynx was so entirely different in form and struc- 
ture from the usual type for the genus that, had it been an 
external character it would long ago have been formed into a 
new genus. 

Karel Thbn^ has demonstrated how in HolothyricUB a single 
internal structure is at variance with the other indications of 
genetic aflBnity. A great many similar instances will be immedi- 
ately called to mind by those who practise dissection. 

Again, if systematists are convinced of the taxonomic value 
of hard parts how comes it that they need to be reminded that 
there are hard parts in the internal anatomy as well which they 
so frequently and habitually leave unnoticed! The endoskele- 
ton of Arthropods, gastric mills, pharyngeal ossicles and carti- 
laginous supports are all systems which might be profitably 
studied by the entomologist and carcinologist, while the con- 
chologist generally proceeds as though the radula and jaw were 
part of the **mush,'' as he so inelegantly terms the viscera. 

Geographicali Distribution 

The advent of the morphologist into the particular sphere of 
systematics or the metamorphosis of the systematist into a mor- 
phologist (it matters not how we put this desirable event) will 
result in .the annexation not only of classification, but also of 
questions of geographical distribution by anatomy and morphol- 
ogy. How many pretty theories in geographical distribution 

iZool lahh., Bd. XXIII, Syst., pp. 720-21. 



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382 TRE AMEBIC AN NATURALIST [Vol-XLVHI 

have collapsed. because they were built on the sands of an in- 
correct classification! The similarity between the faunas of 
South America and Madagascar is supported by many facts, 
but the value of Solenodon in Cuba and Centetes in Madagascar 
has been lessened by the recognition that the two genera re- 
semble each other by convergence, and should now be classified 
in different families. 

The Dendrobatinse also are considered by Dr. Gadow as an 
unnatural group, the two divisions — South American and Mas- 
carene — ^having, according to him, lost their teeth independently. 
Again, Dr. Gadow refers to the Ratitae as a heterogeneous as- 
semblage of birds which is "absolutely worthless" for the 
zoogeographer. There are scores of such artificial groupings — 
the work of the systematist — which have led zoogeographers 
astray. 

The result is that systematic work as at present pursued is 
of very little use to us in the study of geographical distribution. 
It is hopeless nowadays for a zoologist to sit down with a 
list of species and their range and trusting implicitly in sys- 
tematic work to make maps of distribution and, as he so often 
does, to draw deductions therefrom, for the validity of such de- 
ductions must ultimately depend upon the anatomical and mor- 
phological data. Moreover the study of geographical distribu- 
tion is developing new methods of tackling its problems. 

We do not consider it necessary to touch on the other remedies 
that might be applied with a view to redeeming zoological taxo- 
nomy from its present artificial state and to bringing it into line 
with the rest of biology. 

Such remedies — for instance, testing the validity of species 
by genetic experiment and the intensive study of variation — 
have been advocated many times before,* although with little 
success. "We believe, however, that the reforms in descriptive 
zoology we have advocated above are the more urgent. 

«Cf. E. B. Poulton, '* Essays on Evolution," 2. ''What is a Species! " 
and K, Jordan, **Novitates Zoologicie,'' 3, 1896. 



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SHOETEE AETICLES AND DISCUSSION 

NABOURS'S GRASSHOPPERS, MULTIPLE ALLELO- 
MORPHISM, LINKAGE AND MISLEADING 
TERMINOLOGIES IN GENETICS 

In a review of Nabours's breeding experiments with grass- 
hoppers,^ Mr. Dexter makes a distinction between an interpreta- 
tion of Nabours's and his own, where I fail to see a difference ex- 
cept in terminology. This is so typical of much recent Mendelian 
work that I am tempted to call attention to it. 

Nabours describes a cross between a female with characters BI 
and a male with characters CE and comments on the production 
of an individual with characters BEI, He says, as quoted, that 
the ''female parent gave at least one gamete containing the fac- 
tors for the patterns of both her parents (B and I) and that this 
double character gamete was fertilized by one of the E gametes 
which came from the CE male.** 

Dexter prefers to call the supposed exceptional BI gamete of 
Nabours Bcel, and the supposed E sperm which fertilized it hcEi, 
stating that Nabours 's terminology would involve multiple allelo- 
morphism, his own linkage. (Nabours uses, I think, neither ex- 
pression.) Now what is the difference between the two interpre- 
tations! Is it anything but verbal t Is there anything significant 
in the small letters which Dexter has added to Nabours 's form- 
ulae 1 If so, what is their significance t Do they mean any more 
than the extra zeros in the expression 1.000 as compared with 1.0 1 

Dexter proposes an experimental test, that the cross be re- 
peated. '*If then BEI forms should appear again and in these 
when mated to other forms the factors B and I should be found 
to stay together to the same extent as they before separated, it 
would show that close linkage, rather than multiple allelomorph- 
ism explains this particular instance.*' How would it show it! 
If we take Nabours *s assumption that B and I have exceptionally 
gone into a single gamete and formed with E a zygote BI,E, 
would it be counter to his assumption that they should subse- 
quently hang together and that gametes should arise BI and E, 
respectively? Would adding a few small letters to the formulae 
1 Am. Nat., May, 1914. 

383 



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384 THE AMERICAN NATURAL 

alter the case, changing it from multiple alle 
age ? It seems to me that this is one more ca 
ious conclusion is reached in consequence oJ 
for absent characters in Mendelian formulfi 
Wilson has pointed out others. 

BussEY Institution, 
Forest Hills, Mass., 
May 6, 1914 



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Tho Fixation of Chftnctw in Oxganiimi. By Edward 

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Index to Yolnme XLVIL 



CONTENTS OF THE FEBRUARY NUMBER 

Some New Yarietiee of Rati and Gninea-piffi and their 

Relatione to Problemi of Color Inheritanoe. Pto- 

feMor W. E. Castle. 
•* Dominant*' and " ReceMire" Spotting in Mice. C. 

C. Little. 
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oeonrrlng in Field Cultures of Pisum satlTum. 

Dr. J. Arthur Harris. 
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A Genetic Analysis of the Changes pcoduocd by 
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Gynandromorphous Ants, described during tte De* 
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The Effect of Extent of Distribution on I 

Asa C. Chandler. 
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The Origin of X Capsella Bursa pastoris arachnoidea. 
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Biology of the Thysanoptera. II. Dr. A. Franklin 
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Shorter Articles and INscussion : Barriers as to Dis- 
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Kellogg. 
Regeneration, Variation and Correlation In Thyone. 

Professor John W. Scott. 
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Generic Types. Dr.O.F.Oook. 
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Moth. A. H. Sturterant. Nabours*s Breeding 

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▼ox. XLVm, HO. 671 JVLT, 1914 



THE 

AMERICAN 
NATURALIST 



A HOHTELT JOXnUTAL 

Devoted to the Advancement of the Biological Sciences with 

Special Beference to the Factors of Syolution 



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THE 

AMERICAN NATURALIST 

Vol. XLVni July, 19U No. 571 

PATTEEN DEVELOPMENT IN MAMMALS 
AND BIRDS 

GLOVER M. ALLEN, 
Boston Society of Natural History 

The particular coloring of mammals and birds is pro- 
duced by two factors — pigmentation and the physical 
structure of the hair or feathers. Both are often present 
together. In certain mammals, for example the golden 
mole (Chrysochloris) and the European Galemys, a 
beautifully iridescent sheen is produced by the reflection 
of light rays having a certain angle of incidence upon the 
hairs which themselves contain pigment of a character- 
istic color. In the duckbill (Ornithorhynchus) the same 
thing is found. The peculiarity of feather structure that 
causes iridescence is largely developed in certain families 
of birds, as the hummingbirds and the pigeons (see 
Strong, 1904, for an account of the feather structure). 

It is not my purpose to discuss the use of this irides- 
cence to the bird, beyond stating my belief thkt it is in 
part at least for sexual display, as no one can doubt who 
watches the male street pigeon strutting before his mate. 
With amorous coos and lowered head, he confronts her 
and, swelling out his throat feathers, turns about and 
about, so that the light is reflected from his neck and 
throat in a sparkle of rainbow hues. It has also been 
suggested (Thayer, 1909) that iridescence may be a 
strong factor in concealment, since from the variety of 
the colors produced the bird is more diflScult to resolve 
from its many tinted environment amid foliage and 
flowers. 

385 



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386 



THE AMERICAN NATURALIST [Vol. XLVIU 



With many birds the characteristic coloration may not 
be at all that of its pigment. Thus the blue of the male 
indigo bird (Passerina cyanea) is due solely to the phys- 
ical structure of its feathers which though pigmented 
with brown, appear blue by reflected light. If, however, 
a blue feather be immersed in oU and viewed under a 
microscope by transmitted light, it is seen to be broivn- 
pigmented. The physical feather-structure of the adult 
male is thus in this species a secondary sexual character 
chiefly developed during the breeding period. 

The important point at present is, however, that the 
color effects just described are none the less due to pig- 
ment, quite apart from the fact that the apparent color 
of the pigmented area may be different from the actual 
color of the pigment (except that iridescence may some- 
times be faintly seen in an unpigmented feather). 

The use of pigmentation to its possessor is a matter 
still under discussion and investigation. In many cases 
it is doubtless the result of purely physical causes and 
it is quite without the power of the animal to make use 
of its coloration for outward effect. Thus the beautiful 
colors inside the shells of some molluscs are never appar- 
ent from an exterior view, and are supposed by some to 
be in part a waste product, the result of metabolism 
within the organism. 

The present discussion has to do only with the external 
pigmentation of the hair and feathers, respectively, in 
mammals and birds. 

The simplest cases of coloration are those in which the 
body or its covering is everywhere of the same hue, or 
nearly so — as in the elephant, the wild buffalo, or the 
house mouse in which the hairy covering (or hide in the 
elephant) is of a nearly uniform tone everywhere. So 
too, the crow, the apteryx, and the nestlings of many 
birds whose parents show a more highly differentiated 
style of markings. Such mammals and birds, so far as 
the development of pattern is concerned, I would con- 
sider unspecialized, yet it does not follow that in this 



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No. 571] PATTERN DEVELOPMENT 387' 

respect they are also primitive, though in most cases I 
venture to think this 'may be true. The uniformity of 
plumage is probably a derived condition in such a species 
as the Cuban blackbird (Holoquiscalus assimilis) in which 
the duller colored females have yet a yellow patch at the 
bend of the wing, a style of marking widespread among 
allied forms. The adult males, however, have lost this 
and are wholly black. Gadow as well as Keeler (1893) 
conclude that among related species in which there is a 
tendency to differentiation of the coloring the end result 
of the stages through which the species may pass is the 
production of a wholly black bird. In general a wholly 
black condition is no doubt to be considered as a derived 
rather than a primitive state among birds whereas a uni- 
formly dull plumage of a brownish or grayish tone is 
probably in most cases primitive. Among mammals the 
same is probably also true, for in both the black condi- 
tion indicates either an excessive production of the black 
over other associated pigments, or a loss of the power to 
produce the latter, whereas the neutral gray or brownish 
coloring is due to a more even mixture of such pigments. 
As pointed out by Professor W. E. Castle, the ' kicked ^^ 
pattern of the hairs of mammals is probably primitive^ 
and it is certainly very widespread. It is well illustrated,. 
for example, by the house mouse {Mus musculus) or the 
wild guinea-pig (Cavia), in which three separate pig- 
ments occur as granules in the individual hairs — yellow, 
chocolate, and black. These three in their normal mix- 
ture produce a neutral gray tint — mouse color — and an 
examination of this type of coat usually shows that some 
hairs are wholly black, others dark at base barred with 
black and yellowish near the tip. 

There are two ways in which patterns may be developed 
from a uniformly tinted covering of hair or feathers : (1) 
by a local change in the relation of the associated pig- 
ments so that in certain areas only one or two sorts are 
produced instead of three, or only one ; (2) by a failure to 



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888 THE AMERICAN NATURALIST [Vol. XLYIII 

develop pigment at all in certain places, so that a white 
or unpigmented area is produced. 

It is not rare among mammals to find that one or more 
of the characteristic sorts of pigments are not produced 
in certain individuals and probably the factor or factors 
for these are lost altogether from the somatic and sex 
cells alike. Such variations may be perpetuated through 
inbreeding and so no doubt have arisen sundry domestic 
color varieties of animals and plants. For example, in 
the course of experiments with color varieties of the 
house mouse (carried on some years since with Professor 
W. E. Castle) we found that the chocolate-colored mice 
which we bred as extracted recessives from black mice, 
contained only chocolate pigment in their hair, whereas 
in the black parents both black and chocolate pigments 
were present, but the black masked a chocolate pigment. 
Moreover, the chocolate mice always bred true to that 
color, but if bred back to the black parents, gave black 
young or both black and chocolate in Mendelian propor- 
tions, according to the nature of the matings. The inter- 
esting point here is that the chocolate mouse once pro- 
duced, through the loss of its black-and-gray-pigment- 
potentiality, can transmit no other pigment character but 
the chocolate. What causes the occasional production of 
an individual in which one or more of the characteristic 
sorts of pigment is absolutely lacking is still unexplained. 
Nevertheless it is of frequent occurrence not only among 
domesticated species, in which the natural conditions of 
life are so greatly modified, but also in species in a state 
of nature. 

A skunk normally marked, but chocolate instead of 
black, a raccoon likewise of normal pattern but the pig- 
mented areas yellow, are merely examples of the drop- 
ping out of the factor for black pigment from the normal 
combination of the two. Such specimens are of occa- 
sional occurrence, and examples are in the museum of the 
Boston Society of Natural History. Similarly are pro- 
duced red woodchucks or muskrats, or wholly yellow field 



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No. 571] PATTERN DEVELOPMENT 389 

mice (Microtus). Melanism commonly results through 
an excess of black pigment which may mask a second 
pigment. Thus the black hairs of the black variety of 
fancy mouse commonly contain a considerable amount of 
chocolate pigment as well, and so of the hairs of the 
black-appearing skunk. A black mouse thus does not 
contain the yellow pigment, while the chocolate pigment 
is largely masked in general view by the black. In other 
cases it may be that black pigment alone is present. 

It is probable that many cases of dichromatism among 
animals are explicable as similar cases in which one or 
other of the pigments normally present becomes to a 
greater or less degree inactive. Thus red forms of certain 
blackish or dull-colored bats {e. g., the small Molossus of 
Cuba) are apparently the result of the dropping out of 
the factor for black pigment or its great reduction. The 
red and gray phases of the screech owl {Otus asio) are 
probably also explicable as a similar phenomenon. 

It is only when this inactivity of one or more of the 
pigment factors occurs locally on the body that a definite 
color pattern is produced, in which neighboring areas of 
the body are of contrasting hues. As an example may be 
cited the variegated guinea-pigs, whose monotone ances- 
tors are still abundant in a wild state in South America. 
Professor Castle, through his studies of these patterns 
in guinea-pigs, first suggested to me in 1903 that there 
were definite areas of the body which, though contiguous, 
are independent of each other in their pigment-producing 
capacity. In this suggestion lies the key to the chief 
investigation of this paper, namely, the defining of these 
areas, and a study of their behavior in the development of 
pattern by the second of the two methods previously 
given — that is, through the failure of pigment to develop, 
so that white or colorless areas result. This condition of 
partial albinism is not uncommon among animals which 
in their normal condition are completely pigmented. In 
domestic species it is very general and in them tends to be 
preserved. It also occurs normally in the shape of defi- 



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390 THE AMERICAN NATURALIST [Vol. XLVHl 

nite white markings in the patterns of many mammals 
and birds. Magazines of natural history abound with 
instances of total or of partial albinism among mammals 
and birds, either of domesticated or of wild species. 
Some writers have even recognized the fact that such 
white markings tend to occur in certain parts of the 
body, as at the tip of the tail or on the forehead. Darwin 
speaks of the white forehead spot or star, and the white . 
feet so common among horses, and implies that such 
markings must be of some significance. His statement 
on hearsay that white-marked horses are more suscep- 
tible to poisoning from noxious herbs is, however, un- 
corroborated. In 1882, W. H. Brewer gathered a number 
of statistics as to the presence of white marks in horses 
and cows, but reached no conclusion. He could find no 
necessary correlation between the presence or absence 
of white spots in forehead and feet, though it appeared 
that white marks might be more frequent on one side of 
the body than the other. But the tentative conclusion 
that such animals habitually reclined on the side showing 
the more white, is begging the question. 

As briefly stated in my paper of 1904, the important 
thing is not that white tends to appear at certain places, 
but the converse, that pigment production is more intense 
at certain definite centers on the body and the occurrence 
of white or pigmentless areas is due to the restriction of 
pigment formation at the periphery of these centers, so 
that white occurs at their extremities or as breaks b<^- 
tween contiguous color patches. 

In mammals and birds these centers are typically five 
on each side of the body, and a median one on the fore- 
head. They appear to be homologous in both groups, 
though in different species they show varying degrees of 
modification in their behavior and development. When 
a reduction of the pigment areas occurs, the appearance 
is as it were a shrinking of the particular color patch 
toward its definite center. The reduction may vary to 
any degree, from that condition in which the break 



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No. 571] PATTERN DEVELOPMENT 391 

between two adjacent patches is merely indicated by a 
white streak to that in which it is reduced to a small spot 
of pigment, or to zero, when the entire patch drops out, 
leaving a white area. These patches are wholly independ- 
ent of each other in the extent to which they may be 
developed, so that a particular patch may be quite want- 
ing on one side of the body, while its. fellow of the oppo- 
site side is completely developed. Nevertheless, there is 
often a marked tendency to bilateral synmietry in such 
reduction. From a study of partial albinos in which the 
pigment reduction is considerable, the location of the 
ultimate centers of these patches becomes possible as well 
as the determination of their normal extent. I have 
studied several domesticated species in which white 
marks are common, with the results briefly detailed below. 
When all the centers are fully developed the animal is 
completely pigmented; when none is developed, it is a 
total albino. Between these extremes may be found every 
conceivable degree of development. In an ideal case in 
which each center is slightly reduced so as to be circum- 
scribed by white, the animal would have a dark coronal 
or crown patch and a series of five patches on each side 
separated by a median dorsal and a median ventral 
stripe. The anteriormost of the lateral patches center at 
the base of each ear, and each in its greatest development 
covers the side of the head from muzzle to behind the 
ear. These I have called the aural or ear patches; the 
next posterior are the two neck or nuchal patches each 
of which pigments its proper side of the neck, and extends 
from behind the ear to the shoulder and anterior edge of 
the foreleg. When much reduced the patch, as it were, 
contracts to a smaU area on each side of the neck, varying 
slightly in its location among different species. Posterior 
to these come the scapular or shoulder patches one on 
each side of the body. Each pigments the shoulder area 
and foreleg, except (usually) the front edge of the upper 
part of that member. This patch shows interesting slight 
variations in the extent over which it spreads in different 



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392 THE AMERICAN NATURALIST [Vol. XLVHI 

species. Centering nearly at the lower part of the back 
are the pleural or side patches, each of which pigments 
the area from the shoulder to the lumbar region and ante- 
rior part of the hind leg of either side. Last of all, the 
two sacral or rump patches, each of which on its respect- 
ive side pigments the buttocks and tail. In most species 
these two patches are so closely associated that they tend 
to remain fused dorsomedially, so as to give the appear- 
ance, when reduced, of a single median patch at the base 
of the tail. Their frequent bilaterality, however, indi- 
cates the dual origin of such median patches. Each of 
the lateral patches in its complete development extends 
from the mid-dorsal to the mid-ventral line or those of 
opposite sides may overlap slightly. Reduction usually 
first appears mid-ventrally. 

It is probable that the retinas should also be considered 
as an additional pair of patches, since morphologically 
the eye is of dermal origin, and there is sometimes seen 
a tendency to the formation of a small circumorbital 
patch, which appears to break from the ear patch when 
this is largely reduced. 

Pocock (1907) has pointed out that in black-and-tan 
dogs the tan appears about the muzzle, along the sides 
and on the limbs, while the blacker portions are more 
dorsal. It may be added that in tricolor hounds, in which 
the several primary patches are reduced, these are often 
tan color at their several peripheries and black centrally. 
In both cases, the explanation is simply that pigment 
formation is less intense the farther away from the pri- 
mary centers. 

The reason of the division of the body surface into 
these independent areas of pigmentation does not here 
concern me. It is no doubt the result of physiological 
causes, and it is rather suggestive that the several patches 
correspond externally to important nerve centers or 
groups of nerves. Thus the eye pigment corresponds to 
the optic nerve, the aural patch to the auditory nerve, so 
that these two great external sense organs of the head 
have each their corresponding pigment patch. The neck 



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No. 571] 



PATTERN DEVELOPMENT 



393 



patch corresponds with the group of cervical nerves, the 
shoulder patch with the brachial plexus, the side patch 
with the nerves of the trunk, and the rump patch with the 
sacral plexus. It may be further suggested that the 
median crown patch of the head corresponds to the pineal 
eye, a suggestion that is strengthened by the fact that it 
is more or less obsolete in mammals, just as the pineal 
gland is vestigial, whereas in birds, which are more 
reptilian in structure, the patch is usually well defined. 
At all events it is a median unpaired structure, as are the 
pineal and the interparietal bone. 

Turning now to a more detailed consideration of these 
pigment patches in sundry species of animals, we may 
first examine a series of diagrams (Figs. 1-15) of the 







Figs. 1-7. Diagrams Illustrating Pigmentation in the Domestic Dog. 
Figs. 8-15. Diagrams Illustrating Pigmentation in the Domestic Dog. 



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^ 



394 THE AMERICAN NATURALIST [VoL.XLVin 

domestic dog, all of which are carefully drawn from 
photographs or from living animals, and are selected 
from a great number to show various conditions in the 
reduction of the pigment patches. In these and the other 
diagrams the black portions represent pigmented areas, 
irrespective of the actual colors. 

For convenience I have called the white stripes demark- 
ing these chief or primary patches, *' primary breaks/' 
since thiey are the first indications of a decrease in pig- 
mentation such that two adjoining patches no longer 
meet. Secondary or further breaks result in a general 
disintegration of these primary pigment patches, and are 
apparently more irregular in nature, though often they 
follow certain fairly well defined lines. The first of the 
primary breaks generally occur as white patches on the 
chest or belly, about in the median line. These are not 
shown in the dagrams, but in most cases should be under- 
stood as present. In Fig. 1 the pigment areas show a 
beginning in reduction. The two aural patches have 
become separated and their failure to spread to the 
normal limit in the median line has resulted in a white 
nose stripe. A short transverse white marking indicates 
a separation of the neck patch at its anterior edge from 
the ear patch. Elsewhere the various patches are contig- 
uous; but the extremities of th6 limbs and tail are pig- 
mentless, as if pigment had failed to spread to the tips of 
these members in its reduction. In Fig. 2 the same 
primary break between the ear patches is present, and in 
dogs it is one of the first and most frequent to appear. 
The sam^ shrinkage of pigment from the extremities is 
also seen. The neck patch of the left-hand side, however, 
has completely dropped out, and its fellow of the right- 
hand side is reduced posteriorly so that it fails to reach 
the shoulder patch. Thus a white collar is formed. It 
is also interesting to see that at its anterior end a distinct 
constriction is present where the neck patch joins the ear 
patch of the right side. Fig. 3 shows a somewhat similar 
condition but the neck patch of the right side as well as 



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No. 571] PATTERN DEVELOPMENT 395 

the ear patch is missing, while those of the left side are 
fnlly developed. In Fig. 4 both neck patches are missing, 
so that a white collar is formed. In dogs the neck patch 
is usually the first to drop out altogether, so that a white- 
collared dog is of very frequent occurrence. In fox 
hounds this patch is shown unusually well, either wholly 
or partly separated from neighboring patches. The sep- 
aration of the ear patches, wholly or partially, so as to 
produce a white blaze or line in the middle of the forehead 
is about as frequent. In Figs. 8 and 12 a single neck spot 
only (as it happens, in one on the right, in the other on 
the left side) is still present but so slightly developed as 
to be only a small island of pigment wholly separate from 
the neighboring patches. 

The crown spot is so often present in dogs as a little 
oval island, always on the top of the head about in line 
with the anterior bases of the ears (Fig. 4) that I am 
convinced it is a primary patch. It is common in bull 
dogs and bull terriers, and in other breeds is often seen 
but is so commonly not indicated at all, that it seems 
probable it is becoming lost, and its area is filled by the 
ear patches, since these are often separated by a very 
narrow median line only, which, as in Fig. 13, may con- 
tinue posteriorly to separate the two neck patches 
medially as well. In other cases (Figs. 1, 6) the failure of 
the white nose stripe to extend farther posteriorly may 
be due to the persistence of this patch. 

The demarcation of the side from the rump patches is 
indicated by the imperfect primary break across the 
lower part of the back in Fig. 4, while in Fig. 5, a similar 
primary break farther forward indicates the limits of the 
shoulder and side patches. In each case the break is 
incomplete transversely, with a narrow isthmus near the 
median line. In dogs there is a marked tendency for the 
ultimate centers of the side and rump patches to be close 
to the median line, so that the corresponding patches of 
opposite sides are confluent dorsally. This is especially 
the case with the rump patches, with the result that it is 



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396 



THE AMERICAN NATURALIST [Vol. XLVIH 



very rare to see the two rump centers separated, but 
instead, as in Figs. 10 and 14, they appear, when much 
reduced, as a small median spot at the root of the 
tail. That they were originally paired, there is no doubt, 
as there is frequently (as in Fig. 9) a deep median 
notch indicating the median primary break between the 
centers, or (as in Figs. 11, 12) one of the lateral centers 
drops out, leaving its fellow of the opposite side. The 
continued union of the side patches with the shoulder 
patches is seen in Fig. 7, while in Fig. 9, though the union 
is still present between these patches of the right side, on 
the left side the shoulder patch has failed to develop, and 
the side patch is so reduced that it does not meet its 
fellow of the right. In Fig. 8 both shoulder patches are 
present more or less bilaterally equal, and, as frequently, 
are produced into narrow tongues on to the upper arm. 
The two side patches in Fig. 8 are also reduced, so as to 
be wholly separated from each other and from the neigh- 
boring centers. They are further interesting in being 
placed nearly median one behind the other instead of 
nearly opposite. In Fig. 11, on the other hand, they are 
far sundered, but this, in dogs, is a much less usual con- 
dition. In Fig. 10 a single median dorsal patch repre- 
sents the slightly developed side patches, but whether 
this single patch corresponds to one or other of the two 
centers, or whether the two are actually fused in the 
dorsal line, I can not yet say. 

The shoulder centers, when slightly reduced, are large 
in dogs, and cover a considerable saddle-shaped area, as 
indicated in Fig. 5, from near the center of the back for- 
ward including the fore leg and part of the fore shoulder. 
When further reduction takes place the pigment is drawn 
away from the extremities and the saddle separates from 
the neck patch (Figs. 2, 6) and then from the side patch 
(Figs. 5, 9), and finally the shoulder patches separate 
from each other (Fig. 8). One or other of the shoulder 
patches may drop out entirely (Fig. 10) or be reduced to 
a very small spot (Fig. 12) at what may be considered 



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No. 571] PATTEBN- DEVELOPMENT 397 

the ultimate center of the pigment patch, near the upper 
part of the body, near or just back of the shoulder. The 
ear patches seem to be the last to disappear, and these, 
too, may be variously reduced or only one may be present 
(Fig. 15). The approximate outlines of the patches when 
fully developed are indicated by dotted lines in Fig. 15, 
in which 1 is the crown patch, 2 the ear patch, 3 the neck 
patch, 4 the shoulder patch, 5 the side patch, and 6 the 
rump patch. 

In dogs, there is seldom seen any tendency for these 
primary patches to divide. . What has the appearance of 
such a tendency is seen, for example, in the coach dog, 
which is rather evenly flecked with rounded black spots, 
with often in addition, black ears and more rarely reduced 
rump patches. Fig. 9 shows such a dog in which both ear 
patches, one shoulder, both side and both rump patches 
are sharply indicated, though reduced. In addition there 
are present on the white body areas between, many small 
flecks of dark color, evenly distributed, which are clearly 
not islands separated from the primary patches. Indeed 
this spotting seems to constitute a wholly different cate- 
gory of pigment formation, in addition to that of the 
primary patches, which latter I have called ''centripetal" 
pigmentation. As Professor Castle suggests to me, it is 
probably homologous with the ''English" marking or 
spotted condition of domesticated rabbits, and possibly 
the dappling of horses is a similar phenomenon. When 
these spots and the primary color patches are of the same 
hue, it is not possible to distinguish the two in visual 
appearance, unless the latter are reduced areally, when, 
as is sometimes the case in the coach dog, one or more of 
the primary patches is seen with the spots, as it were, 
proliferating from its edge. This second element no 
doubt enters as a factor in the color pattern when the 
small spots are of a different color from that of the 
general body surface, as in case of the cheetah {Cynce- 
lurus) or the leopard and jaguar. 

I am inclined to think that the excessive breaking up of 



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398 



THE AMERICAN NATUBALIST [Vol. XLVIU 



the primary patches, to be considered under the cow, is 
not a wholly similar phenomenon. 

Five diagrams illustrating the domestic cat are shown 
in Figs. 16 to 20, and are interesting to contrast with 




Figs. 16-20. Diagbams Illustbatinq Piombntation in the Domestic Cat. 

those of the dog, also a carnivorous mammal. The 
demarcation of the primary patches is usually less sharp 
than in dogs, but is in general similar. The most comnion 
appearance is where the primary breaks occur in the 
mid-line below, giving a white throat, chest or belly; or 
the separation of the aural centers produces a white 
streak on the nose or extends it up between the ears. 
The ear patches in Figs. 17, 19, 20, show successive reduc- 
tion, so that at first the hinder margin of the ears, as in 
dogs, becomes white, then with further decrease in pig- 
ment production, the inner bases only are colored. The 
neck patch has its ultimate center farther back than in 
dogs so that when much reduced, it is present as a pig- 
mented spot at the very base of the neck or even at the 
front of the shoulder (Figs. 16, 17). In Fig. 16 the neck 
patch of the right-hand side is only slightly reduced and 
is in contact anteriorly with the ear patch, while poste- 



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No. 571] PATTERN DEVELOPMENT 399 

riorly it does not meet the shoulder patch. The left-hand 
neck patch, however, is quite separate from the neighbor- 
ing patches and is reduced to a small area at the junction 
of the neck with the shoulder. It is absent in Fig. 17 from 
the left side and is represented on the right side by a 
similar small center, placed far back. In Fig. 20 the 
neck patch or patches show a reduction to a single small 
square median patch at the base of the neck, but whether 
this represents a median fusion of the two lateral centers, 
or whether one only has persisted and has shifted to the 
midline, I do not attempt to say, though the former 
hypothesis seems on the whole more probable. 

The shoulder patch in house cats is relatively small, 
and, as indicated by the indentations in Figs. 17, 18, is of 
the fore side of the upper arm, but the shoulder patch 
when fully developed seems to cover the rest of the leg 
and a smaU scapular area. It is shown much reduced in 
Fig. 19, on the right-hand side, and is altogether wanting 
in Fig 20. The conjoined shoulder and side patches in 
Fig. 18 are shown reduced laterally, so as to form a 
broad median stripe which I take to mean that the ulti- 
mate centers are closely approximated dorsally. The 
neck patch is wholly absent, but both ear patches are 
present and joined medially. The sacral patches, as 
commonly, seem fused or at least very close together. 
There is a small break midway on the tail, which sepa- 
rates off a pigmented tip, a phenomenon which I shall 
refer to under ** centrifugal pigmentation.^^ The side 
patch is long comparatively, and extends forward to 
cover the deficiencies of the shoulder patch, as in Fig. 17. 
Here the left side patch has been reduced at its anterior 
end, and its separateness from the patch of the right side 
is indicated by the median indentations. It is often want- 
ing in domesticated cats. 

The sacral patches, pigmenting the buttocks and tail, 
seem to be fused or closely approximated at the root of 
the tail, as in dogs. I have seen no instance of the crown 
patch being shown in the cat, though such may occur. 



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400 THE AMERICAN NATURALIST [VoL-XLYIII 

The approximate boundaries of the five bilateral patches 
are indicated in Fig. 20 by dotted lines ; 2 is the ear patch, 
3 the neck patch, 4 the shoulder patch, 5 the side patch, 
and 6 the rump patch. 

Among domesticated rodents the pigment patches have 
been studied in rats, house mice, and guinea-pigs. In 
all, the same patches appear except that in rats and mice 
the median crown patch appears to be lost, though in the 
guinea-pig it is often present. Diagrams of parti-colored 
mice are shown in Figs. 21-24, and sufficiently indicate 



Fios. 21-24. Diagrams Illustrating Pigmentation in Domestic Varibtibs 
OF THE House Mouse. 

the primary pigment areas. The white spot on the fore- 
head of Fig. 21 indicates a primary break between the 
two ear patches, and varies widely in different individ- 
uals, from a few white hairs only to a large blaze The 
inheritance of such a blaze has been studied by Little 
(1914). The white mark at the base of the neck in Fig. 
21 indicates the beginning of separation of the neck from 
the shoulder patches and perhaps of the two neck patches 
from each other, because of its longitudinal extension. 
The white band across the neck in Fig. 23, however, 
indicates probably only the beginning of a separation of 
the neck from the shoulder patches, which in Fig. 24 has 



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No. 571] PATTERN DEVELOPMENT 401 

wholly sundered these two areas, so that a white-collared 
mouse results. The condition shown in Fig. 22 is similar, 
except that the separation has taken place on the right 
side only, between the neck and the shoulder patches of 
but one half of the body. A break between the two neck 
patches of opposite sides is further indicated in this 
figure by the deep median reentrant back of the ears. 

In all four diagrams the areal restriction of the 
shoulder patches is shown, but in varying degrees. In 
Fig. 21, the pigment has not spread to the feet, leaving 
these white, and so in the other figures, but to a greater 
degree. A median linear break between the shoulders 
indicates the restriction of the patches of opposite sides 
at this point, which in Fig. 22 is more clearly perceptible. 
The posterior limits of the shoulder patch are further 
shown in this diagram, by the beginnings of a break 
between the shoulder and the side patches. In Fig. 24 
this break is no longer interrupted, but clearly separates 
the two areas. Further, the side patch has dropped out 
on the left. In Fig. 23 an imperfect separation of 
patches on the posterior part of the body has taken place. 
On the right-hand side the shoulder patch, which in mice 
is of considerable extent, has broadly separated from the 
side patch, while on the left-hand side a long transverse 
break has taken place between the side and the rump 
patches, with two island-like white spots between, the 
anterior of which probably marks the transverse line of 
stress between shoulder and side patches, the posterior 
the median line of breaking between the two side patches. 
A slight indentation in the pigmented area far back on 
the right side of Fig. 22 points to the beginning of restric- 
tion between side patch and rump patch. The separation 
of these patches by a transverse mid-dorsal break is 
shown in Fig. 21, and their complete separation on the 
left side appears in Fig. 23 (the transverse white mark), 
while in Fig. 24, owing to the failure of the left-hand 
pleural patch to develop, the two rump patches, both par- 
tially separate from each other, are wholly disconnected 



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1 



402 THE AMERICAN NATURALIST [Vol. XLVIII 

from the former except by a narrow isthmus on the right 
side. The long tail is usually without pigment, or mainly 
so where areal restriction is present, and it is seldom that 
pigment extends far on to the base of this member when 
the restrictive tendency appears. In the domesticated 
varieties of rats, the same patches may be distinguished. 
There is, however, an interesting variety known as the 
''hooded" rat, in which the ear and neck patches appear 
to be normal, but a narrow median dorsal area is pig- 
mented for a varying length, sometimes quite to the root 
of the tail. A separate factor seems here to be involved, 
producing what may be called a ''centrifugaP^ type of 
pigmentation, which in many forms of mammals causes a 
black spine stripe {Sorex wardi, Tupaia tana, certain 
forms of Apodemus, Equus caballus), and others. 

Among guinea-pigs the typical primary patches are 
beautifully shown and may be seen in sundry figures 
published in papers by Professor Castle on heredity in 
this animal. The guinea-pig is one of the few mammals 
yet known in which the median crown patch is visibly 
present, a character which I take to be primitive. 

In guinea-pigs the breaking up of the ticked color 
pattern has progressed under long domestication to an 
extraordinary degree, so that not only are black, tawny 
or grizzled animals produced in various shades, but even 
in the same individual, the different primary pigment 
areas may he of different colors. This fact is of much 
significance, for it indicates liot only the mutual independ- 
ence of the contiguous color areas, but further points to 
the manner in which a variegated color pattern may have 
been acquired. Among mammals the color pattern is in 
general, not greatly developed in comparison with birds, 
yet in many cases where some modification has taken 
place, it is evident that this differentiation is confined to 
the limits of one or two of the primary pigment patches. 
Thus in the South American Tayra (T. harhara)^ the 
head and neck are a grizzled gray, and the breaks occur- 
ring in pied individuals show that the grizzled condition 



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No. 571] PATTERN DEVELOPMENT 



403 



a.sr 




j^ 





n 





3X 
Figs. 25-32. Diaobams Illustbating Pigmentation in Horses. 



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404 THE AMERICA^ NATURALIST [Vol. XLVHl 

is confined to the aural and nuchal patches only, for else- 
where the animal is black. In this case, too, the black 
condition is probably derived, for youngish animals are 
uniformly grizzled, and sometimes, apparently, this is 
the adult condition as well. 

Among domesticated ungulates the same primary 
patches are to be distinguished in cases where partial 
albinism renders their bounds apparent, with the excep- 
tion that in horses, cows and deer I have seen no clear 
indication of the median crown patch which in mammals 
is probably obsolescent. 

In both horses and cows the patches show interesting 
and peculiar modifications. A series of diagrams (Figs. 
25 to 32) show these patches in ''calico^' horses, though 
not so fully as could be wished. The first indications of 
areal restriction of pigment in horses appear in the shape 
of a white ''star" or round spot in the center of the fore- 
head. This is often accompanied by white at the base of 
the hoofs, or sometimes the entire foot is white producing 
the so-called ''white stockings." But there is no neces- 
sary correlation between these white areas, such as 
Brewer (1882) tried to show. The white on the forehead 
may vary from a few white hairs to a broad blaze cover- 
ing the entire front of the head between the eyes to the 
muzzle. Sometimes the restriction of pigment is such as 
to produce in addition to the white star on the forehead, 
a white spot over each eye, and sometimes these three 
spots are joined by a narrow unpigmented area. This 
indicates that pigment production is weak at a spot 
directly over the eye in comparison with neighboring 
parts, and this no doubt accounts for the fact that 
in black-and-tan or other dogs these are the pale spots 
over the eyes where black pigment is not produced. 
A white spot over the eye is also characteristic of many 
rodents. 

Next after the restriction of the ear patches and the 
drawing away of pigment from the feet, the most comimon 



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No. 571] 



PATTERN DEVELOPMENT 



405 



white marking seems to be a primary break, as in Fig. 25, 
from the shoulder back of the foreleg, which delimits the 
posterior border of the shoulder patch. In the horse the 
shoulder patch is large, and differs from that of any 
mammal I have yet studied, in its great extent forward 
along the dorsal side of the neck nearly to the head. In 
Fig. 26 a small break at the back of the neck indicates the 
beginning of separation between the ear and the neck 
patches dorsally, and a long tongue of white running up- 
ward from the forearm indicates the anterior limit of the 
shoulder patch. This limit is marked still nearer the 
dorsal line in Fig. 27 by a white spot on the side of the 
neck near its base. In Fig. 28 the shoulder patch has 
entirely dropped out and the white space outlines very 
nearly its extent. The ultimate center is perhaps shown 
by the small shoulder spot in Fig. 31. 

The area covered by the ear patches extends well on to 
the upper part of the neck, and in Fig. 29 is shown at its 
greatest spread, or, as in Fig. 28, cut off by a narrow white 
collar from the neck patch. The neck patch is remarkable 
from the fact that in its areal reduction it becomes re- 
stricted first dorsally, and the ultimate center of each side 
is nearly ventral on the throat, so that, as generally seen^ 
the two centers form a single median patch on the front 
or ventral part of the throat. In Fig. 26 the neck patch is 
seen to pigment the anterior side of the forearm and is 
partly separated from the shoulder patch by a long 
tongue of white. It seems to extend up diagonally to 
reach the mid-line of the neck for a short distance only, 
as indicated in Fig. 28, where its bounds are only slightly 
contracted. In Fig. 29 it is so far lessened as to be absent 
from the forearm, though still in contact at the throat 
with the ear patch where, however, a deep indentation 
locates the dividing line between the two patches. In 
Fig. 31 a median ventral division of the conjoined neck 
patches is seen indicated at the upper part of the area, 
which in this case no longer reaches the ear patches. 
Still further reduction of both ear patches and neck 



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406 THE AMERICAN NATURALIST [Vol. XLVm 

patches is seen in Fig. 32, but, as commonly, the neck 
patches seem fused in the midventral line. This shifting 
of the neck centers ventrally is a rather remarkable 
phenomenon which may have some relation to the manner 
in which the head is held erect. For this reason it might 
be expected also in antelopes, and is perhaps evidenced 
in such a species as the oryx, in which there is a black 
median line on the throat as though strongest pigment 
production centered there rather than on the gray sides 
of the neck. The median reduction of the shoulder 
patches in horses is sometimes indicated by a white mane. 

The rump patches in the horse appear to be much as in 
other mammals, restricted to the tail and posterior part 
of the buttocks and the entire foot. In Fig. 30 the patch 
is shown at nearly its full development, except that it has 
failed to extend to the entire hind foot. In Fig. 27 it has 
drawn away still farther but remains in contact with the 
side patch at one place. In Fig. 29 it is further restricted 
to the tail and posterior border of the haunches, while in 
Fig. 32 it covers only the root of the tail and that member. 

The side patch is the largest of all and extends from 
the shoulder to the fore part of the haimches and on to the 
fore part of the hind leg nearly to the foot, as seen in Figs. 
27 and 28, where it is still in contact with the rump patch, 
or in Fig. 29 where it has become separated. In its fur- 
ther reduction this patch may appear as a small spot 
back of the ribs or, as often, a curious division takes 
place, separating the patch into a dorsal area and a 
lateral one. Occasionally this secondary break appears 
in a horse which has most of its patches otherwise well 
developed. In Fig. 31, the pigmented area of the tail, 
buttocks and lumbar region consists of the conjoined rump 
patch and a dorsal portion of the side patch, while the 
ventral part of the side patch is present as the oval spot 
at the groin. In Fig. 30 the latter spot only persists, but 
in Fig. 32 the dorsal portion of the side patch alone is 
present as a stripe along the entire back, except where it 
breaks away posteriorly from the small rump patch. 



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No. 571] 



PATTERN DEVELOPMENT 



407 



This peculiarity of the side patch in horses is somewhat 
paralleled in cows by a tendency to secondary breaking 
up, though in a different way, as detailed below. It is 
significant in this connection that in horses and donkeys 
there is usually a black stripe along the spine from 
shoulder to tail which may indicate that *' centrifugal pig- 
mentation" is also present (see beyond). The dotted 
lines in Fig. 32 indicate the approximate boundaries of 
the several primary patches. The crown patch seems to 
be wanting in horses ; 2 is the ear patch, 3 the neck patch, 
4, 5 and 6 the shoulder, side, and rump patches, 
respectively. 

Of domestic ruminants I have studied the pigmentation 
in the cow and show in Figs. 33 to 42 a few of the many 



Figs. 33-36. Diaqbams Illustbatino Pigmentation in Domestic Cows, Side 

View. 

variations in partial pigmentation. These are all drawn 
from photographs or from the animals themselves, and 
are of cows in which, so far as I know, there has been no 
attempt at breeding for pattern. Two types of spotting 
may be distinguished in cows : first, that in which the pig- 
mented areas are sharply outlined and solid or at least 



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408 THE AMERICAN NATURALIST [Vol. XLUVQ 

practically so; second, that in which there is a grefiLteTr < 
less tendency for the primary patches to be much, bxro'k 
np into small islands (as in Fig. 36) by secondary l3x*^ct' 
though the main areas are still distinguishable. I tt 
this second or fragmental type to be a different pXx^xxc 
enon from the diffuse or dappled condition seen, ixx 
coach dog or the dappled-gray horse. 

In the cow, the ear patches as usual pigment ^^c^lx 
proper side of the head to a short distance behimd 




Figs. 37-42. Diaqbams Illustrating Pigmentation in Domestic C^^^ . 
Seen Spread Out and from Above. 

ears. The point of separation between ear patchy ^ ^ 
neck patches is indicated by a small break back ^:>^ - 
skull in Fig. 38, while the posterior extent is sho^*^'"^'^ -. 
the two ear patches in Fig. 42. These patches uS"*^^ 



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No. 571] PATTERN DEVELOPMENT 409 

draw apart first across the forehead making here a tri- 
angular white mark, and on the muzzle, as in Fig. 34. 
Further restriction broadens these white marks and joins 
them by a narrow isthmus as in Fig. 35. In Fig. 40, the 
two patches are still conjoined across the vertex, but are 
much reduced, that of the right side more than that of the 
left. In Fig. 42 they have failed to join medially, though 
fairly well developed longitudinally. Still greater re- 
duction, as in Fig. 37, confines them to the ears, the bases 
of which appear to be the ultimate centers. 

The neck patch in the cow is more extended posteriorly 
than in the horse, and its center is strictly lateral rather 
than nearly ventral. It is shown in Fig. 34 somewhat 
contracted from the mid-line of the throat, but extends 
squarely back against the f oreshoulder at the base of the 
neck, and is fused near its ventral comer with the 
small shoulder patch, itself much reduced. As in 
other mamimals it appears to extend in its complete 
development, to the front edge of the upper foreleg. The 
animal in Fig. 41 shows a bilaterality in its pigmentation 
that is rather unusual. What appear to be the reduced 
neck patches are seen far back at the border of the fore- 
shoulder. In Fig. 40 the left-hand neck patch has 
dropped out, but that of the right side is still present, 
though small, and in Fig. 42 it is reduced to a small spot 
only. 

The shoulder patch in cows is remarkably narrow, 
and compressed between the neck patch and the body 
patch, whence it extends as usual on to the foreleg. In 
Fig. 33 a primary break back of the f oreshoulder marks 
the nearly vertical posterior outline of the shoulder 
patch. In Fig. 34 the separation of this area from the 
neck patch is all but complete and the patch itself some- 
what reduced. Its narrow vertical outline is thus indi- 
cated, as well as in Fig. 39, in which there is a narrow 
tongue-like extension down on to the center of the foreleg. 

In its further reduction it appears as a small center 
at the base of the scapula, as in Fig. 35, or in Fig. 40, in 



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410 THE AMERICAN NATURALIST [Vol. XLVIK 

which both shoulder patches are present, though small. 
In Figs. 41 and 42 the shoulder areas are wanting. A 
very common mark in cows is a white belt just back of 
the foreleg. This is due to the development of a primary 
break between shoulder patches and side patches, a con- 
dition which is nearly realized in Figs. 33 and 38. It is 
probable that this marking has been more or less fixed 
through selection in breeding, and this has been the more 
readily accomplished, since this break occurs in a place 
which is one of the first in cowa to cease pigment 
production. 

The side patch is large and covers the entire lateral 
region of the body from the scapula to the hips, and on 
to the front edge of the hind limb. When only slightly 
reduced, it appears as a blanket-shaped area across the 
back as in Fig. 38, where it has not wholly broken away 
from the shoulder and rump patches, or as in Fig. 33, 
where it has become nearly separated. In its further 
reduction this dorsal blanket shows a peculiar manner of 
breaking up into more or less transverse stripes directed 
slightly backward. The beginnings of these secondary 
breaks appear in Fig. 39 in which are seen on each side 
posteriorly two deep indentations at the edge of the 
patch, whose points if extended would meet the white 
pigmentless islands already present within the patch. 
In Fig. 34 a similar series of indentations points to the 
trisection of the side patch which is realized in Fig. 35. 
Here is a characteristic which if developed might even- 
tually result in the actual production of white stripes on 
the body, such as are found, for example, in certain ante- 
lopes as the bongo and the kudu. The tendency of the 
side patch to divide into three, as in these diagrams, is 
rather marked in cows, and even with further reduction 
the three centers persist fairly well. The first of these 
secondary centers is just back of the shoulder patch, the 
second about over the last ribs, and the third over the 
lumbar region. In Fig. 40 the first two are present on the 
left side, with a small spot between, which has become 



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No. 571] PATTERN DEVELOPMENT 411 

separated from one or the other of them, while the third 
or lumbar spot has dropped out. On the right side, the 
first and second divisions are still fused dorsally, but 
the lumbar division is distinct. The same three divisions 
are seen in Fig. 35, better developed, whereas in Fig. 42, 
the two lumbars are present, on6 on each side, and con- 
siderably in advance of them, what seem to be the rem- 
nants of the first division of the side area, the left one of 
which has further broken up. 

The rump patches show no especial peculiarities, but 
cover the posterior part of the buttocks and hind legs, 
and the entire feet and tail. Though frequently the two 
patches of opposite sides are conjoined medially, they are 
often, under considerable reduction, well separated. The 
beginning of such a separation appears in Fig. 38, where 
there is a deep median tongue of white anteriorly, mark- 
ing the line of union. In Fig. 41 the reduction has pro- 
gressed still farther so that the two patches are quite sun- 
dered medially and do not extend to the tail. In Fig. 40 
the patch of the left side has become inactive, and that of 
the right si(jle is small. 

A curious condition not infrequently seen is shown in 
Pig. 37, in which all the patches are present, but those of 
the right side are separated from those of the left by a 
median dorsal white line, showing the distinct bilaterality 
of these pigment areas. In the figure, the ear patches 
are so restricted as not to reach the neck patches of 
their respective sides, the shoulder patches do not extend 
far on the forelegs, the side patches are reduced ven- 
trally, and the rump patches, though in contact with the 
side patches, do not pigment the tail or extremities of 
the legs. A further reduction of pigment areas results in 
Fig. 41, in which the paired centers of neck, side and 
rump patches still appear. 

The diffuse condition of pigmentation is illustrated in 
Fig. 36, which is a photograph, inked in. The ear patch 
is seen much reduced, but pigmenting the ear. The neck 
patch is of most irregular shape, with several subsidiary 



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412 THE AMEBIC AN NATURALIST [Vol. XLVHl 

spots separated from its lower border. A clear line 
separates the neck patch from the shoulder patch, which 
is also of most irregular boundary. The side patch, at 
its fore part, is broken into a series of small islands 
which tend to arrange themselves in lines following the 
direction of the ribs. The main part of the patch shows 
a decided tendency to break into the usual three or per- 
haps four portions. It is common for cows to have 
patches with very irregular boundaries and tongues of 
pigment, which may break oflf into isolated spots in a 
most bewildering fashion, but even in such cases it is 
possible to distinguish the main patches of which these 
form part. 

White patches occur in other domesticated ungulates 
as the pig, the llama, the alpaca, the camel, the yak, the 
reindeer, and the goat. In the water-buflfalo, occasional 
animals seen in Egypt show a beginning of pigment re- 
duction through the presence of white in the forehead or 
on the tail. I have had no opportunity to study the mark- 
ings of these species. 

(To he concluded) 



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INTERNAL RELATIONS OF TERRESTRIAL 
ASSOCIATIONS 

ARTHUR G. VESTAL 
University of Colorado 

Contents 

I. Introduction. 
11. Internal activities of the association, as determined by the con- 
stitution of the individual organism. 

A, Ecological constitution of the organism. 

B, Constitution of the plant in relation to environment. 

C, Constitution of the animal in relation to environment. 

D, Internal activities of the association. 

III. Belative influence of different organs with the association domi- 
nance. 

A. Factors of dominance among animals. 

B. Criteria of dominance among animals. 

C. Specialized and unspecialized animals. 
IV. Distribution within the association. 

A, Distribution in space. 

B, Distribution in time. 

V. Interdependence of terrestrial plant and animal commimities. 

A, Geographic relations of terrestrial plants and animals. 

1. Greographic range: the province. 

2. Distribution within the province: distribution of plants 

and animals into communities. 

B, Local relations of plant and animal assemblages (relations 

within the association). 

1. Similarity of ecological type of plants and animals. 

2. Belative dependence of plant and animal assemblages. 

3. Correspondence in distribution within the association. 

4. Uniformity of species composition of plant and animal 



VI. Summary and conclusions 
VII. References. 

I. INTRODUCTION 

The material here presented is based on the writer ^s 
studies, during the past five years, of terrestrial associa- 
tions of plants and animals, mainly in different parts of 
the prairie region. The particular area chiefly used for 
illustration in this paper is the sand prairie of the. Illinois 
Eiver valley, plants and animals of which have been 
studied by Hart and Gleason (1907) and by the writer 
(19136). A later study has been made of the vegetation 
of inland sand areas of Illinois (Gleason, 1910) ; the Ijake 
Michigan beach area in northeastern Illinois has been 
studied by Gates (1912) ; beach areas in Illinois and Indi- 
ana by the writer (1914a). The chief representation of 

413 



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414 THE AMERICAN NATURALIST [V0L.XLYIII 

the sand prairie is the bunch-grass association, well- 
developed in parts of northwestern, central and north- 
eastern Illinois, and in northwestern Indiana, in each 
of which areas, as well as in the sandhills of Nebraska 
and of eastern Colorado, the writer has studied. Discus- 
sions of physical, vegetational and animal aspects of the 
associations of the central Illinois sand prairie, together 
with an annotated list of the animal species, with data on 
food, habitat-relations, life-history, etc., are embodied in 
the writer's paper (19136), to which constant reference 
is made. Frequent citations to a more detailed study of 
local distribution of grasshoppers, in a Michigan area 
(Vestal, 1913a), and to the many associational studies 
of Shelford, are to be found. 

Th« data which have accumulated relate nearly equally 
to the botanical and zoological aspects of associational 
study, but since the subject of plant ecology is at present 
more advanced than that of animal ecology, it has been 
possible to treat the vegetational side of the problem 
very briefly, so that more of the discussion relates to 
animals and animal assemblages. 

The writings most frequently cited are indicated by 
italic capitals, the full titles appearing in the list of spe- 
cial references at the end of the paper. 

The writer wishes to thank Dr. Charles C. Adams, Dr. 
Max M. Ellis and Dr. H. A. Gleason for suggestions and 
criticism. 

11. INTERNAL ACTIVITIES OF THE ASSOCIATION, AS DETER- 
MINED BY THE CONSTITUTION OF THE 
INDIVIDUAL OIWJANISM 

The internal activities of the association may be said 
to be the sum-total of the activities of all the plants and 
all the animals which make up the association. Such a 
sum-total of activities may well be thought of as an intri- 
cate and complicated mass of dependencies. It wiU 
simplify the treatment of the entire system of relations 
if the chief dependencies of the individual organism are 
first discussed. A knowledge of the ecology of the asso- 



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No. 571] 



TERRESTRIAL ASSOCIATIONS 



415 



ciation is built up largely from a knowledge of the ecol- 
ogy of all the organisms which compose it. 

A. Ecological Constitution of the Obganism 

The constitution of the organism is the sum-total of 
those of its characters which enter into relation with 
environment. These are commonly classified as structural 
and physiological. For the purposes of this discussion 
it would seem preferable to subdivide physiological char- 
acters, restricting the term physiological to denote those 
characters concerned with ordinary metabolic processes 
of the organism, and excluding those having to do with 
life-history and rates of reproduction (these may be dis- 
tinguished as biographical and numerical) and also, when 
dealing with animals, those related to behavior {psycho- 
logical characters). The constitution of the organism in 
relation to environment will be discussed in terms of 
these classes of characters. 

B. Constitution of the Plant in Relation to 
Envibonment 

The environmental influences in the association are of 
three kinds: (1) physical, (2) plant, (3) animal. Each 
plant and each animal must obtain from each of these 
three constituents of its environment certain necessaries ; 
it has certain structural and physiological characters 
which enable it to obtain these necessaries, and to with- 
stand adverse environmental influences. 

The environmental relations of plants are very differ- 
ent from those of animals. A tabular comparison of 
these relations has been made by Shelf ord {A: 593). As 
therein pointed out, structural characters are of greatest 
importance in the adjustment of the plant to the environ- 
ment, and plants in a given habitat are likely to have a 
common structure or growth-form, indicating common or 
ecologically equivalent physiological conditions within. 

Different plants (and different animals), within a com- 

1 Based partly on Forbes ', classification of adaptation to food require- 
ments (1909: 292). 



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416 THE AMERICAN NATURALIST [VoL.XLVm 

mon habitat, are similar in ecological constitution (eco- 
logically equivalent) in so far as their presence is deter- 
mined by the same environmental conditions. It should 
be pointed out that there are local environmental differ- 
ences within the area of the association which allow the 
presence of differently constituted organisms, and that 
the entire range of environmental conditions within the 
habitat is usually much wider than that of the environ- 
mental complex selected by a particular organism. The 
environmental complex of the organism is not the same 
as the sum-total of environmental conditions withm the 
association. Each organism differs in greater or less 
degree from others in ecological constitution, and thus 
selects a different environmental complex. 

The physical factors of the environment are of great- 
est importance in the life of the plant. Plants influence 
one another directly to only a slight extent. There is 
usually very little of the social relationship among eco- 
logically similar plants which will compare with such 
relationships as seen in animals. Competition among 
plants is mainly a struggle to determine which plants 
are to be most favored by physical conditions, and it is 
probably most severe for the physical factor present in 
minimal quantity. In desert associations plant competi- 
tion is almost exclusively for water, and extensive root 
systems are developed. In grassland it is very largely 
for above-ground space ; in forests it is principally for 
light. The influence of the animal-environment is prob- 
ably of greater importance than has commonly been 
realized by plant ecologists ; the study of economic ento- 
mology and of the effects of grazing upon grasslands is 
helping to bring about a realization of the importance of 
animal influence upon plant life. 

The structures of plants show frequent and great 
modification in response to the physical conditions of the 
environment. These modifications are most frequent and 
important with respect to the factor present in minimal 
quantity. Characters which may be associated with 



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No. 571] TERRESTRIAL ASSOCIATIONS 417 

direct plant influence are infrequent. Certain plants 
which become more abundant as a result of close grazing 
are equipped with spines, or have acrid or pungent 
juices; and many other characters may be correlated 
with animal influence. The structural modifications are 
most evident in the adjustment of the plant to external 
conditions, though these are accompanied by physiolog- 
ical characters which are also in harmony with the en- 
vironment. 

C. Constitution of the Animal in Relation to 
Envibonment 

The animal, like the plant, selects an environmental 
complex which is of three kinds: (1) physical, (2) plant, 
(3) animal. Different animals show extreme variation 
as to the degree in which the different parts of the en- 
vironment are important to their existence. Endopara- 
sites, for example, are most directly concerned with the 
animal part of their environmental complex. 

The existence of any animal is dependent upon a num- 
ber of physical factors, all of which must be present in 
proper degree or quantity. Minimal and maximal quan- 
tities of any one of several factors mark the limits of 
existence of any animal {A: 598 — law of toleration of 
physical factors). It is not necessary to consider these 
factors in detail. The animal reacts to physical environ- 
ment most evidently by its behavior : psychological char- 
acters restrict activities more narrowly than do those of 
other types. They are accompanied by structural and 
physiological characters; hibernation, storage of food, 
etc., are biographical characters correlated with seasonal 
changes in physical environment. Animals which are 
subjected to very severe physical conditions may produce 
a larger number of offspring than those to which physical 
conditions are favorable. This is an example of corre- 
lation of a numerical character with the physical environ- 
ment. 

The plant environment reacts upon and modifies phys- 
ical and animal environments, and has also direct influ- 



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418 THE AMERICAN NATURALIST [VoL-XLVHI 

ence upon the animal. In addition to its effect in the con- 
trol of temperature, light and other physical factors, the 
vegetation constitutes the basic food-supply for the ani- 
mal community, and also provides shelter and materials 
for abode {A: 601). Cases of direct association between 
particular plants and particular animals are numerous, 
but the majority of animals have no direct relation to 
particular kinds of plants. Behavior characters are in 
general of greater importance in the relation of the 
animal to the plant environment, though such relations 
are not confined to psychological characters. 

There are two sets of relations between the animal and 
its animal environment. These are: (1) social, and (2) 
antagonistic. Social relations {inter-psychology and 
inter-physiology of Shelf ord. A: 608, h) include those 
between individuals of the same species, and between 
animals of the same or similar mores^ (ecologically equiv- 
alent animals), in so far as these relations are not 
antagonistic. Breeding and family relations are the 
principal activities which come under this head. Be- 
havior characters are of greatest importance, as compared 
with structural and other characters. The antagonistic 
relations constitute the intermores-psychology and phys- 
iology of Shelf ord {A : 608, c) . They are the antagonistic 
relations between animals not ecologically equivalent, and 
they are also antagonistic relations within a species and 
between ecologically similar forms. These relations are 
probably not greatly concerned with reproduction, but 
center about the feeding activities of the animal. The 
existence of the individual animal, in its relation to other 
organisms, is dependent upon three conditions: (1) it 
must obtain suitable and suflScient food, (2) it must be 
free from destructive competition of animals of similar 
requirements, (3) it must be able to escape or to with- 
stand attacks of other animals (or, sometimes, of para- 
sitic fungi or bacteria). The various characters of the 

2 Mores (Latin for customs, habits) has been used bj Shelf ord (1911a: 
30) to supply the need for a term including all physiological and behavior 
characters of the animal. 



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No. 571] TERRESTRIAL ASSOCIATIONS 419 

animals are correlated with all three of these conditions. 
The characters are both *' adaptive'' (fixed by heredity), 
and regulatory (not fixed). 

Following is a synopsis of correlations between the 
various types of characters and the three conditions of 
existence, in the relation of the animal to its antagonistic 
animal environment. 

(I) Characters Which Enable the Animal to Obtain Food 

1. Structural Characters. — ^Animals of selective food- 
habits often have specialized structures, as in the case of 
the long tongue of woodpeckers. Animals of non-selec- 
tive food-habits have mouthparts that are not so highly 
specialized ; thus grasshoppers and cutworms have heavy 
mandibles for cutting vegetation; tiger-beetles and 
Chrysopa larvae have sharp piercing mandibles. The 
whole structure of the predaceous animal, its *' action 
system," is sometimes suggestive of the manner of pur- 
suit or holding of its prey. 

2. Physiological Characters. — The physiology of ani- 
mals of different food-habits differs materially. Physio- 
logical characters are not apparent, generally speaking^ 
and are secondary to psychological characters. The 
range of food assimilable by the animal is usually much 
wider than that selected by it, as is seen when animals of 
selective habits take new kinds of food when the usual 
food is exhausted, often thriving seemingly as well as. 
before. 

3. Psychological Characters. — Selection of food is 
determined chiefly by behavior characters of the animal. 
These may be so widely variable that the animal will be 
virtually omnivorous, as in the case of crickets, or so 
narrowly restricted that it eats only a single species of 
plant or animal, as the leaf -beetle Blepharida, a sand- 
prairie insect eating leaves of the three-lobed sumac, and 
the pentatomid bug, Perillus, which feeds on Blepharida 
(cf. E: 49, 30). Selection is only one of the many psycho- 
logical characters relating to food. The behavior cnar- 
acters manifested in obtaining food are of great variety. 



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420 THE AMERICAN NATUBALIS I [VoL.XLVlIT 

With these are accompanying structural and physiolog- 
ical characters, which, however, play a subordinate part. 

4. Biographical Characters. — These may consist in 
timing the life-history of the animal with that of the 
food-species (plant or animal) in such a way that the 
period of greatest activity of the former coincides with 
the period of greatest growth or abundance of the latter. 
This feature may be incidental to seasonal change of 
physical environment. Whatever its cause, it is very 
general in an established association, so general that it 
is seldom recognized. It is of advantage to both animal 
and food species. 

5. Numerical Characters. — The rate of reproduction 
must be so adjusted to its food-supply (plant or animal) 
*Hhat only the unessential surplus of this food shall be 
appropriated, leaving the essential maximum product 
undiminished'' (Forbes, 1909: 293). Species of re- 
stricted food-habits must remain less numerous in indi- 
viduals than general feeders, as the available food-supply 
is very much less. 

(II) Characters Which Remove the Animal from the 
Competition of Other Form^ 

1. Structural Characters. — Structures which permit 
animals to live in varied habitats, to take varied foods, 
or to time their activities differently, remove each group 
of animals from competition of all the others, resulting 
in advantage to all. To that extent the f ossorial forelegs 
of the mole, the long proboscis of the butterfly, and modi- 
fications of the eyes of nocturnal animals, are characters 
which do away with competition. The structural char- 
acters are, however, accompaniments of modifications of 
behavior, and are secondary to the latter. 

2. Physiological Characters. — Ability to digest food- 
materials unavailable to other animals is an advantage- 
ous physiological character. Thus the leaf-beetle Chry- 
sochus auratus, which lives on dogbane (Apocynum)^ 
and the ** skin-beetle " Trox, which eats animal tissues 
in an advanced stage of decomposition, have few corn- 



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No. 571] TERRESTRIAL ASSOCIATIONS 421 

petitors for food. Physiological, as well as structural, 
characters, are accompaniments to modifications of habit. 

3. Psychological Characters. — Apparent preference 
for certain activities, certain habitats, or certain foods, 
together with peculiar behavior complexes, seem to be of 
greater importance in removing animals from competi- 
tion than structural and physiological characters. 
Highly regulatory habits permit certain animals to ad- 
just themselves to changing conditions of competition. 

4. Biographical Characters. — ^Professor Forbes (1909: 
295-298) discusses the alternative timing of the active 
period among close competitors for food. (It so happens 
that the animals mentioned, having almost identical 
habits, compete with each other in many ways, besides 
with respect to food.) In the sand prairie it has been 
found that different species of certain genera, having 
otherwise the same habits, differ greatly in life-history. 
Evidence of this biographical adjustment is more or less 
complete for two species of Arphia {E: 21), two or three 
species of Hippiscus {E: 21), two species of the milkweed 
beetle, Tetraopes {E: 47), and three species of P recta- 
canthus, robber-flies {E: 55). In these genera the term 
of activity of one species is abruptly followed by that of 
another, the successive periods usually covering most of 
the summer season. 

5. Numerical Characters. — ^When a certain limited 
food, place of abode, or other desideratum is used by two 
or more kinds of animals at one time, a numerical adjust- 
ment is likely to be found among these competing species. 
The rate of multiplication of each species must be suffi- 
cient to keep up its numbers, to allow it to hold place 
with competing species. (Too high rates of multiplica- 
tion, on the other hand, are disadvantageous because of 
other influences.) 

(Ill) Protective, Defensive and Concealing Characters 
1. Structural Characters. — Animals have various de- 
fensive, protective and concealing structures. Stings, 
beaks, mandibles, teeth, claws, hairs, spines, resemblance 



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422 TBE AMEBIC AN NATURALIST [Vol. XLVIH 

to surroundings in color or form — all are of advantage to 
animals which possess them. Certain of the interstitial 
or blowsand animals resemble in color the sand on which 
they rest (Cicindela lepida, Stachyocnends, Psinidia, 
Spharagemon; ci. E). 

2. Physiological Characters. — Malodorous and ill- 
tasting animals are to a considerable degree exempt from 
attack. This is essentially a physiological modification, 
though a structural basis in the form of glands may be 
present. In the sand prairie Chrysopa (lace-winged fly), 
a number of Hemiptera, ladybird beetles, soldier bugs 
{Chauliognathus) J blister-beetles (Epicauta), and others, 
are ill-tasting (perhaps not to some animals). The 
skunk's lack of caution is well known. 

3. Psychological Characters. — Self-preservation in 
animals depends more upon their activities and behavior 
than upon special structures. The ordinary methods of 
resisting or evading attacks of enemies are generally 
known and need not be discussed. Many specialized in- 
stincts have arisen, such as feigning death, or dropping 
to the ground when disturbed, as seen in many herbi- 
colous beetles. 

4. Biographical Characters. — It is to the advantage of 
animal species preyed upon by others if their period of 
greatest abundance is timed with the period of greatest 
activity of the animals which feed upon them. 

5. Numerical Characters. — Animals, as well as plants, 
must produce a normal excess in numbers which will pro- 
vide food for other animals and still leave a sufficient 
number of individuals to continue the species. 

It will be noted that the various kinds of characters 
usually accompany one another, all being parts of a 
single modification. This modification may have rela- 
tion to one or to several of the environmental influences 
(physical, plant or animal) or to more than one kind of 
antagonistic relation between the animal and others. 
The modification is not necessarily advantageous to the 
animal with respect to all or to any features of the 



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No. 571] TERRESTRIAL ASSOCIATIONS 423 

environment, though a large number of characters do 
result in advantage. Characters advantageous in one 
relation may be disadvantageous or indifferent in an- 
other relation. The origin of the characters is not at 
present a subject which can be treated in a study of inter- 
relations of organisms (cf. Shelf ord, 19126: 342). Be- 
havior characters appear to be of greatest importance to 
the animal in determining its relations with other organ- 
isms of the association, though usually these are accom- 
panied by physiological or structural characters. The 
animal is not adapted to a particular status in the asso- 
ciation ; its ecological constitution determines what place 
it shall be able to find among the other animals of its sur- 
roundings. The relations among the various animals, 
when a state of equilibrium has been reached, are the 
result of mutual accommodation on the part of all the 
animals involved. 

D. Internal Activities of the Association 

It has been indicated that the complex of activities 
within the association is the synthesis of all the activities 
of the individual organisms. Each plant and each ani- 
mal is subjected to physical, plant and animal influences. 
From the extreme complexity of the entire system of 
relations within the association, it is hardly possible to 
consider more than one or several of these at one time.^ 
It is possible, however, to see that each species finds a 
status within the association, according to its particular 
combination of internal and external relations. It con- 
tinues in fairly constant numbers from year to year. A 
change in these numbers, if at all great, may cause a dis- 
turbance in the association, which is quickly regulated 
by the activities of conflicting organisms (Forbes, 1880). 
The entire association of plants and animals, by very 

• Very helpful diagrams are given by Shelf ord (C: 167, 168) which il- 
lustrate the food relations of land (prairie) animals. There are also dia- 
grams showing food relations of aquatic animals (C: 70, 71). Food rela- 
tions of animals of plains and mountain streams are discussed by Ellis 
(1914: 122-127; diagram on p. 125). References to studies dealing with 
interrelations of organisms may be found in the recent handbook of Adams 
(1913: 123 et seq.). 



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424 THE AMERICAN NATURALIST [Vol. XLVm 

reason of the conflicting interests, the varying conditions 
necessary for existence, and the varying methods of re- 
sponse to these conditions, forms a self-contained and 
self-regulating system of activities. 

III. RELATIVE INFLUENCE OF DIFFERENT ORGANISMS WITHIN 
THE ASSOCIATION— DOMINANCE 

The plant ecologist determines which plants in an asso- 
ciation are of greatest importance (dominant) by ob- 
serving which species tend to increase at the expense of 
others, which are most abundant, most frequent, largest, 
etc. Competition among plants in a grassland associa- 
tion is mainly for space, and the dominant species are 
usually determined with considerable accuracy after some 
study. With the animals the consideration of dominance 
involves greater complexity. The important relations 
between conflicting animal species are those in which 
they obtain food, are removed from competition, or 
escape enemies. These relations are in each case most 
directly concerned with food. The plant-eaters of the 
association thus form a dominant group within the asso- 
ciation, since predaceous and parasitic animals, and 
scavengers in large part, depend upon them for existence. 
Individual species within the various food-groups, how- 
ever, present such striking differences in importance, 
that we can not speak of all plant-eaters as dominant 
forms, or that all animals of other food-habits are un- 
important. It is merely probable that the phytophagous 
group will contain a larger proportion of dominant spe- 
cies. This appears to be the condition in the bunch-grass 
association. 

A. Factors of Dominance Among Animals 

The success of an animal species within an association 
is due to the resultant effect of a large number of factors. 
Among these may be mentioned number of individuals, 
size, activity, voracity, concentration of food, rapidity of 
growth, rapidity of reproduction, and wideness of dis- 
tribution in space and in time. Dominance signifies more 



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425 



than mere ability of a species to thrive in its surround- 
ings : the species of greatest influence are those on which 
the greatest number of other animals depend ; thus domi- 
nant species are successful, but successful species are not 
always dominant. Species which are relatively free from 
competition or which have comparatively few enemies 
may be successful, but are not dominant, and are usually 
not numerous. Species which are successful and at the 
same time extremely abundant, usually form the food of 
a large number of other animals, as it appears to be the 
rule that no considerable source of food within the asso- 
ciation is left unused. Dominance in a species, then, 
would seem to include the dependence of other animals 
upon it, plus the ability to thrive in spite of the drain 
upon its numbers. 

B. Critebia of Dominance Among Animals 

The factors mentioned as contributing to the success 
of a species, and the numbers of animals dependent upon 
the species, are all indications of the degree of its domi- 
nance. It appears that another criterion is available, 
which perhaps expresses the summation of many factors 
which contribute toward dominance. This is the degree 
of specialization exhibited by the species in its adjust- 
ment to a particular place in the association. Dominant 
animals appear to be those of moderately specialized 
habits rather than those of highly specialized, or rela- 
tively unspecialized, habits. 

C. Specialized and Unspecialized Animals 

Each species may be referred to a position in the scale 
of specialization in habit. The degree of specialization 
of the species is well seen in the food-habits, though all 
the habits are to be considered. The most abundant food 
in the sand prairie is plant material, bunch-grasses. The 
majority of the plant-feeders are adapted to eat herbage 
of nearly any kind : they are not restricted to particular 
species or particular parts of plants. They are non- 
selective feeders. Grasshoppers,, cutworms and certain 



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426 THE AMERICAN NATURALIST [Vol. XLVm 

leaf -beetles are thus moderately specialized plant-eaters. 
There are also non-selective predaceous animals, as tiger- 
beetles and lycosid spiders, which eat any kind of small 
animal. These are also moderately specialized. The 
moderately specialized animals carry on the gross metab- 
olism of the association; they constitute the dominant 
group, and include the dominant species. 

Selective feeders belong with the highly specialized 
animals. In the bunch-grass association Languria hi- 
color, an erotylid beetle, bores in the stems of the com- 
posite Cacalia (Indian plantain), while Lygceus bicrucis 
(hemipterous) feeds on the same plant; Perillus circum- 
cinctus eats Blepharida rhois. Others of the associa- 
tion eat selectively. The majority of parasites are 
greatly restricted in their selection of hosts. Such ani- 
mals are particularly dependent upon special kinds of 
food, which in many cases are not available to general 
feeders. Highly specialized forms are thus enabled to 
avail themselves of opportunities denied to animals of 
generalized type; but while they avoid competition by 
the adoption of special kinds of food, or by special habit 
of some other kind, they lack the versatility of the les§ 
specialized animals, being unable to adjust themselves 
to changed conditions. They may, therefore, become 
abundant at times ; but as they depend wholly upon one 
variable condition (perhaps the presence of a particular 
plant species, which may be quite infrequent) they never 
can become dominant species. Absolute numbers of the 
insects which live upon Cacalia, for example, are insig- 
nificant in comparison with such animals as the grass- 
hoppers. 

On the other hand, animals of relatively non-specialized 
habits would also be ineffective in the association, for 
whatever field of activity they were to enter, they usu- 
ally would find already occupied by some animal better 
constituted for that activity. Such non-specialized forms 
would assume particular importance only when some 
animal on which they might feed should become unusually 



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No. 571] TERRESTRIAL ASSOCIATIONS 427 

abundant. Few animals are really non-specialized in 
habits; many moderately specialized species, however, 
may on occasion turn from their ordinary activities, per- 
haps to appropriate a particularly abundant kind of food. 
Many ants are thus habituated to certain ordinary kinds 
of food, but are able to eat organic food of almost any 
sort, and do vary their food with circumstance. When, 
as frequently happens, some animal species becomes very 
abundant,* the attacks of a great many species of flexible 
habits becomes concentrated upon it, and the numbers of 
the food-species are soon reduced to normal. Animals 
with non-specialized habits, by taking whatever food is 
easiest of access, act as regulators of disturbances within 
the association. A clear exposition of the manner in 
which species of generalized habits restore unbalanced 
conditions to equilibrium is given in a paper by Forbes 
(1883), in which the regulative action of birds upon 
insect oscillations is discussed. 

The animal's status within the association is deter- 
mined not only by its food-habits, but by the sum-total of 
its physiological and behavior characters (its mores). 
The degree of dominance is indicated not merely by the 
degree of specialization of food-habits, but in all habits, 
by the degree of flexibility of behavior. An extreme 
specialization in nearly any behavior character, as habit 
of abode in the pit-digging ant-lion larva, prevents the 
species from becoming dominant. The degree of spe- 
cialization of behavior is thus a convenient criterion of 
the relative influence of animals in the association. The 
dominant animals are moderately specialized, and carry 
on the ordinary work of the association. The highly spe- 
cialized animals make use of space otherwise unoccupied 
and food material not demanded by other species. Cer- 
tain of the first group, with habits more highly regulatory 
than is usual, with perhaps some few unspecialized forms 

^ With some animale sudden abundance is a matter of seasonal periodic - 
itjf as in the case of May-flies (Hexagenia) along the Illinois Biver (E:17). 
The adults on emerging become a sudden source of food for animals of ad- 
joining terrestrial associations, as the bunch-grass. 



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428 THE AMERICAN NATURALIST [VoL.XLVin 

in addition, tend, by following the path of least resist- 
ance, to act in opposition to forces tending to destroy the 
biotic equilibrium. 

IV. DISTBIBUTION WITHIN THE ASSOCIATION 

The association may be subdivided into minor groups 
of organisms, both in space and in time. Each group, 
being thus removed from the immediate influence of the 
others, is to some extent self-contained, having its own 
environmental conditions, its own assemblage of organ- 
isms, and its own system of interrelations. 

A. DiSTBIBUTION IN SpaCE' 

Different parts of the space occupied by an association 
present different environmental conditions. In the ver- 
tical distribution, four strata, the air (cf. E: 73), the 
plant layer, the surface layer and the underground layer, 
are usually present. In forest associations, the plant 
layer is complex, plants of various heights giving rise to 
minor strata (cf. ^). In grassland associations the plant 
layer is relatively uniform. Animals are most numerous, 
during the feeding activity, in the plant layer. Others 
find food at the surface or underground. Many of the 
animals in the air or on the ground move about rapidly 
from plant to plant. Predaceous animals (while active) 
are frequently permanent members of air and ground 
layers, depending for food upon the transient animals 
and upon members of their own group. The ground 
stratum is composed of the surface and subsurface layers 
{E: 72), which are not, however, continuous horizontally, 
but alternate to greater or less extent. 

Local variability in horizontal distribution is due 
partly to local discontinuity of the various strata. This 
interruptedness is particularly conspicuous in open asso- 
ciations, where the plants do not form a dense growth, 
but are separated by open spaces. The subsurface area 
is provided by cover of various kinds, which lies more or 
less scattered about on the surface. 

»Cf. Shelf ord, A, B, 1912&, C; aleo D: 167; also p. — of thin paper. 



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No. 571] TERRESTRIAL ASSOCIATIONS 429 

The motility of the animal allows change in stratum, 
and to some extent and in some animals, in habitat, with 
change in activity. The food-stratum and the food- 
habitat are apparently of greatest importance in the rela- 
tion of the animal to other organisms. 

B. DiSTBIBUTION IN TiME 

Physiological activities of the plants are subject to 
diurnal variation, and are also greatly affected by varia- 
tions in weather conditions. The greater part of the 
animals of an association are active during the day. 
Others are nocturnal. During the inactive period of the 
day the animal rests in some more or less sheltered place, 
perhaps in a burrow or nest. The inactive state is also 
induced by unfavorable weather conditions. 

Seasonal changes in the association are very great in 
temperate climates, particularly in treeless regions, 
where the winters are severe. Seasonal changes in 
the vegetation are marked, certain groups of the 
plants appearing in successive periods during a sum- 
mer season, giving four or five successive aspects to the 
plant cover. A corresponding seasonal distribution is 
observed among the animals of the association (cf. D: 
175). 

Annual changes in the associations are indicated by 
the very marked differences in the numbers of indi- 
viduals, in certain species of plants and animals, in suc- 
cessive years. This may be due (1) to fluctuation in the 
numerical adjustment between different organisms, and 
(2) to the effect of annually varying phenological condi- 
tions upon the various organisms. 

Oscillatory irregularities in the association take place 
at indefinite intervals. The causes and nature of oscilla- 
tions have been thoroughly treated in several of Forbes 's 
writings (1880, 1883, 1887). 

V. INTERDEPENDENCE OF TEBBESTBIAL PLANT AND ANIMAL 

COMMUNITIES 

The thesis of the following section is that, in terrestrial 
climatic or extensive environments, the relations between 



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430 THE AMERICAN NATURALIST [Vol. XLVTU 

the assemblage of plants and the assemblage of animals 
are intimate and regular of occurrence; so much so that 
(1) the two are coextensive, (2) the two constitute to- 
gether a community which may be called a biotic asso- 
ciation, (3) neither plant nor animal assemblage usually 
occurs independently of the other, (4) the geographic 
distribution of many of the plant and animal species 
which make up the assemblages are in general corre- 
spondence, (5) the species composition of the association, 
over its range, varies no more widely, relatively speak- 
ing, than would an assemblage of plants alone. Perhaps 
the single view-point of the botanist, on one hand, and 
the zoologist, on the other, has tended to a neglect of the 
dual character of the one problem. Probably most botan- 
ists and zoologists agree that relations of animals and 
plants within a habitat are most intimate, and there is 
a tacit assumption that all the organisms in one place 
constitute the true system of interrelations, but botanists 
have spoken of plant communities, and zoologists of 
animal communities. There are numerous disharmonies 
and variations in agreement of plant and animal assem- 
blages, but these must not be allowed to obscure general 
facts of correspondence. 

It is recognized that .plants and animals of an area of 
essentially homogeneous physical conditions are inter- 
dependent, the animals as a group being wholly depend- 
ent upon the plants for food, and many of the plants 
being directly dependent upon animals, as in the matter 
of pollination. All are directly or indirectly affected by 
animals in some way. It is also recognized that the 
plants are a good index to conditions for animal life, the 
plant assemblage affecting animals locally in modifica- 
tion of the physical environment, and more directly in 
providing food, shelter, etc. {A: 601). It is further ac- 
cepted that plants and animals respond to general en- 
vironmental conditions in similar manner (Craig, 1908). 
Thus considered, the character of the plant population of 
an area is an index to general character, or ecological 



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TERRESTRIAL ASSOCIATIONS 



431 



type, of the animal assemblage. These relations, how- 
ever, are quite general, lacking detail. Detailed consid- 
erations may be geographic, including geographic range 
of species and of communities, and the distribution of 
species and of individuals into communities; and they 
may also be local, dealing with interrelations of plants 
and animals within the area of the community. 

A. Geogbaphic Relations op Tebrestbial Plants 
AND Animals 

1. Geographic Range: The Province. — ^If one were to 
plot the geographic range of the plant species found to- 
gether in a given climatic habitat, a general correspond- 
ence in distribution would be made apparent, a large 
number of the species ranging more or less continuously 
over a common, rather definite area (cf. Transeau, 1905). 
The similar ecological constitution of these plants and 
their consequent selective distribution into similar envi- 
ronmental complexes gives a uniformity to the vegeta- 
tion over the geographic region in which these environ- 
mental conditions are found, and the resulting vegeta- 
tion unit is known as a vegetation province (Gleason, 
1910 : 42). The area of the province is generally uniform 
in physical conditions. This uniformity is only relative, 
being subject to gradual geographic variation in climate, 
perhaps giving rise to subregions in distant parts of the 
province, and to abrupt local variations in soil, water- 
content, exposure, etc., giving rise to local or edaphic 
plant assemblages very different from those of the cli- 
matic or geographic type. Thus the prairie province 
occupies the winter-dry interior region of North America. 
Environmental variations from east to west, climatic and 
physiographic, divide the province into the three sub- 
regions of Pound and Clements (1898). Certain plant 
species range over one or all of these subregions, still 
others establishing themselves over the whole area of the 
province and also scatteringly eastward, in dry treeless 
parts of the deciduous forest province, to the Atlantic 
coast. These last are also typical prairie plants, though 



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432 THE AMEBIC AN NATURALIST [Vol. XLVHI 

extra-limital in parts of an adjoining province locally 
approximating the prairie environment. 

The habitat-selection of different animal species re- 
sults, in precisely the same manner, in similarity of geo- 
graphic range among ecologically similar animals. These 
correspondences of distribution point to the existence of 
definite areas characterized by general similarity of the 
animal assemblages. As the physical factors of the en- 
vironment are the same ultimately for animals as for 
plants, and as the vegetational environment for animals 
has the same range as the physical environment, we 
might expect animal communities to have the same geo- 
graphic distribution as plant communities, and we might 
expect the area of the plant province to be characterized 
by distinctive kinds of animals as well as by distinctive 
kinds of plants. The province is thus not simply a vege- 
tation province, but a hiotic province. This is not a 
new notion. Euthven (1908: 388-390) has stated a cur- 
rent viewpoint as follows : 

Those who are acquainted with the literature of the field zoology of 
North America are familiar with the fact that, since the time of the 
Pacific Railroad surveys, naturalists have noted that there are in North 
America well-defined biological regions. These have been pointed out 
at various times by Allen, Cope, Merriam, and others, and the fauna of 
each has been more or less investigated. . . . For example, we have forms 
of birds, reptiles and mammals characteristic of the southeastern de- 
ciduous forest region, and still others characteristic of the northeastern 
coniferous forest region, etc. 

Shelf ord {A: 604) bases his classification of animal 
regions upon that of plant regions, as worked out by 
Schimper (1903) and Transeau (1903, 1905). 

How close the correspondence of distribution of par- 
ticular animals with that of vegetation provinces may be, 
is well shown in the case of North American rabbits 
(Nelson, 1909). The distribution maps shown for certain 
species and groups of these animals might almost serve 
as maps of the provinces. Many other animals, verte- 
brate and invertebrate, correspond in area with the plant 
provinces. Among the insects listed by Hart (1907 : 205) 



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No. 571] TEBBESTRIAL ASSOCIATIONS 433 

as western species, those for which a number of locality 
records are available are plainly to be assigned to the 
prairie province, the range of most of them extending 
west to the Eocky Mountains, north about as far as 
Montana, east to Illinois or Indiana, and south to Texas. 

Other animal species bear apparently no relation to 
province boundaries. Such animals have been discussed 
by Shelf ord {A: 606, footnote), who shows them to be of 
three types: (1) Species of scattered but very wide 
range, covering perhaps several plant realms (animals 
of local associations of extreme habitats) ; (2) Species 
occupying only a part of the plant realm in which they 
belong (animals of such ecological constitution that their 
range is restricted by some conditions unfavorable in 
certain parts of the province) ; (3) Species occupying 
intermediate ground between two realms — these are few 
(Euthven). These exceptional species are found also in 
plants, so that local associations are occupied by both 
plants and animals of the scattered-but-wide type of 
range, while certain subregions, as the Great Plains area 
of the prairie province, contain associations with both 
plant and animal species restricted to these less extensive 
areas. 

Associations of two adjoining provinces may inter- 
grade^ if ecologically similar, or may alternate if dis- 
similar. Similar associations of two provinces may con- 
tain the same or closely related species, as with certain 
grasshopi>ers which range in both northeastern and west- 
em coniferous provinces {D: 173). But these same asso- 
ciations contain also plant species in common, so that 
irregularities of range are no greater in animals than in 
plants. 

2. Distribution Within the Province: Distribution of 
Plants and Animals into Communities, — It is seen that 
plant and animal species may correspond closely in geo- 
graphic range. There may be also more local corre- 
spondence in distribution. The plant community has 
been found by the writer to be the convenient index of the 



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434 THE AMERICAN NATURALIST [VoL.XLVni 

area of the habitat for animals. It has been observed, 
in an area in Michigan, that grasshopper species corre- 
spond closely in local distribution with plant communities 
(/)). There is evidence that local distribution of ani- 
mals is seldom promiscuous as a result of motility (D: 
159). It appears also that the local variability of envi- 
ronmental conditions within the area of the climatic plant 
community is suflSciently great, usually, to supply all 
necessary conditions for a large number of animals, so 
that the limits of the plant community need not be 
passed, ordinarily. 

The animal community of the area may be thus, in large measure, self- 
contained, and coextensive with the plant community (D: 161). 

One of the problems of plant ecology has been the 
differentiation of plant communities or associations. 
Mere comparison of lists of species is not sufficient; rela- 
tive abundance of various species must be considered as 
well. Animal assemblages in contiguous areas must be 
separated in the same way. Given two adjoining habitats 
differing in plant population, it has been found that, in 
addition to differences of animal species,® there are also 
differences of relative abundance in those animal species 
common to the two areas {D: 154, 167). 

The local area of a plant community is determined by 
(1) local distribution of the physical environmental com- 
plex, and (2) influence (competition, etc.) of adjoining 
plant communities. Local area of the animal community 
depends upon (1) local distribution of physical environ- 
ment, and (2) local distribution of vegetational environ- 
ment, the latter being uniform over the area of the plant 
community. Contiguous areas differing in physical and 
vegetational conditions will be expected to differ also in 
animal population, in a degree comparable to that of the 
differences in environmental conditions. 

Physical habitats, and plant communities, sometimes 
alternate, sometimes intergrade ; it is not unreasonable to 
expect accompanying alternation or intergradation of 

« Differences in species, both plant and animal, are accompanied l>y dif- 
ferences in ecological constitution. 



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No. 571] TERRESTBIAL ASSOCIATIONS .435 

animal populations. Certain of the animal assemblages 
of sand habitats, as studied in central Illinois, intergrade ; 
others, as oak forest and bunch-grass, differ radically. 

The above considerations, if correct, appear to signify 
that, in ordinary climatic development of plant and ani- 
mal life in temperate land environments, the area of the 
animal assemblage is that of the plant assemblage, both 
resting basically upon the physical environment. The 
plant and animal assemblages are therefore coextensive 
parts of a biotic association, composed of both plants 
and animals, and this association as a whole constitutes 
the real terrestrial community of living organisms. 

B. Local, Eelations of Plant and Animal Assemblages 
(Eelations Within the Association) 

The more intimate relations between plants and ani- 
mals are ^een in the detailed study of a single associa- 
tion. The bunch-grass association of sand prairie is 
selected for illustration (E: 68). 

1. Similarity of Ecological Type of Plants and Ani- 
mals. — Shelf ord has shown {A: 593-594) that animals 
and plants may evince ecological similarity by similar 
response to the same general environmental conditions, 
behavior responses in animals^ corresponding to struc- 
tural responses in plants,® so that mores of the animal 
may be in accord with growth-form in the plant. Shel- 
ford states {B: 87) that ''plants and animal communities 
are in full agreement when the growth-form of each 
stratum of the plant-community is correlated with the 
conditions selected by the animals of that stratum.'' 

In the bunch-grass there is general agreement, ac- 
cording to this criterion. The herbaceous stratum is oc- 
cupied mainly by tuft and mat plants — bunch-grasses, 
cactus and a few half-shrubs. Associated with the tuft or 
mat growth-form is the sedentary mores of the plant- 
inhabiting animals (leaf -beetles, stem-borers, ambush- 
bugs, etc.). A considerable proportion of ground surface 

. 7 Or motile organisms, cf. C: 305. 
• Or sessile orjj^nisms. 



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436 THE AMEBIC AN NATUBALIST [Vol. XLVEI 

is bare sand; in the interspaces between the dommant 
plants are slender annuals (interstitial plants), and here 
are also found animals of the roving mores of the ground 
stratum (interstitial animals). Many of these are swift- 
running and predaceous (six-lined lizard, tiger beetles, 
lyeosid spiders). 

Correspondence in ecological type of plants and ani- 
mals in the bunch-grass is not complete in several re- 
spects. Shelf ord mentions types of disagreement {B: 
88; C: 306-308), and there is a further important kind of 
disharmony, in mixed associations, due to presence of 
diverse types of plants and animals {D: 163). Mixed 
associations are quite frequent in forest border regions, 
and in the transition area between two provinces. The 
plant and animal assemblages of a given habitat, partic- 
ularly if climatic and extensive, are usually in general 
ecological agreement, and the exceptions are likely to be 
infrequent or temporary (Shelf ord, B: 88). 

2. Relative Dependence of Plant and Animal Assem- 
blages. — There is evidence that the agreement of plant 
and animal assemblages of terrestrial associations is 
often a matter of accommodation on the part of the 
animal assemblage. In the early stages of development 
of vegetation, local physical conditions dominate; in 
later stages the vegetation assumes the type determined 
by climatic conditions, and exerts nearly complete con- 
trol over local physical factors. In established associa- 
tions, therefore, the locally dominating environmental 
feature is the vegetation. Shelford states that in the 
several associations of a successional series, the domi- 
nating animal mores are correlated with the dominating 
conditions {B: 94) and that, as the forest increases in 
density, the animals make use of the vegetation in in- 
creasing degree, particularly for breeding-places, and as 
places of abode {B: 90). Many grasshoppers of open 
grassland depend upon a particular kind of soil for egg- 
laying, while those of closed forest lay eggs in fallen 
logs — a condition of the plant environment (D: 163). 



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TEBBESTBIAL ASSOCIATIONS 



437 



The sand-prairie vegetation is in an intermediate stage, 
certain animals depending chiefly on the presence of 
loose bare sand, others on the bunch-grass vegetation. 
With development of bunch-grass into closed grassland, 
the interstitial animals are eliminated. The animals of 
established associations, while in accord with climatic 
physical conditions, are perhaps more intimately affected 
by vegetation conditions. Since established associations 
are very much more extensive than primitive associa- 
tions, the importance of vegetation as a dominating part 
of the environment for animals becomes apparent, and 
we may conclude that the character of the plant assem- 
blage determines, to a large extent, the ecological type 
of the animal assemblage. 

3. Correspondence in Distribution within the Associa- 
tion. — The uniformity of physical and vegetational con- 
ditions is only relative. There are spots in the bunch- 
grass association in which local invasion of blue grass 
has occurred, darkening and binding the soil. In such 
partly humified situations, small colonies of the corn- 
field ant, not occurring elsewhere in the bunch-grass {Er 
57), have been found. There are also areas some few 
feet in diameter in which the bunqjies of grass are few, 
small and scattered. In these relatively bare patches the 
abundance of interstitial animals is greatly increased. 
More direct relations are seen in the case of animals 
associated with particular species of plants. Within the 
association, any animal species, like any plant species, 
may be distributed generally throughout the area, or it 
may be restricted to a part of the area characterized by 
a slight environmental difference, or it may occur in 
scattered parts of the association, characterized by 
scattered local differences {D: 168). There is evidence 
that, in so far as the vegetational environment is con- 
cerned, distribution of animals within the association is 
usually a direct function of similar distribution of plants. 

4. Uniformity of Species Composition of Plant and 
Animal Assemblages. — It has been seen that plant assem- 



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438 THE AMEBIC AN NATURALIST [Vol. XLVHI 

blages of definite ecological type, as regards growth- 
form, etc., are regularly accompanied by animal assem- 
blages of similar ecological type, as regards mores. In- 
terest attaches also to the problem whether associated 
plant and animal assemblages show definite species 
relations. 

One familiar with a certain association, who visits a 
representation of that same growth in a different part 
of the same climatic region, will be struck with the fact 
that a large proportion of both plant and animal species 
is well known, while a certain proportion, perhaps con- 
siderably smaller, is new to him. The writer has been 
impressed with the similarity of the plant and animal 
populations of the sandhills of central Nebraska and of 
eastern Colorado, to those of the sand prairie of central 
and western Illinois, despite the fact that certain species 
are not common to the two areas. Tiger-beetles, blow- 
snake, grasshoppers, box-turtle, six lined lizard, western 
meadow-lark, white-footed mouse, among the animals; 
prickly-pear, lead-plant, bunch-grasses, sand-bur, sand 
evening primrose, among the plants; are represented' in 
the two areas either by the same or by closely related 
varieties and species. There are no yuccas or sand-sages 
in the Illinois sand prairie, no lizard Holbrookia nor 
lubber-grasshopper Brachystola; and there are certain 
eastern species not found in the western sandhills. But 
on the whole the species (particularly the important 
species) common to the two areas are more numerous. 
This is the more remarkable in view of the fact that dis- 
tribution of sand prairie is discontinuous, the largest, 
nearly uninterrupted gap being several hundred miles in 
extent. Many of the animals, as well as plant species, of 
dry mixed prairie-grass in loamy soil, are the same along 
the mountain-front in Colorado (Vestal, 19146) as in 
north-central Illinois. The likenesses become much more 
impressive as distance is decreased. 

Absolute identity of species composition, where large 
numbers of species are involved, is an ideal condition. 



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No. 571] TERRESTRIAL ASSOCIATIONS 439 

never actually attained. No one can say just what pro- 
portion of species-in-common is necessary for two 
growths to be said to represent the same association. In 
addition to likenesses and differences of environment, of 
aspect, and of history, which must be weighed, the differ- 
ent plant and animal species vary so mtch in importance 
in the association, in physiological variation and in range 
of environmental tolerance, that associations can hardly 
be separated or placed together on a statistical basis. A 
comparison of species is fair if the following kinds of 
plants and animals are left out of consideration; (1) 
those of limited range within the climatic region or prov- 
ince, including species belonging more properly to other 
provinces; (2) those of very indefinite habitat-relations, 
which are found in nearly any kind of habitat; (3) those 
of special restricted habitats, which may be scattered 
about in many kinds of associations, as moist dead wood, 
in which particular fungi, beetles, perhaps snails, myrio- 
pods and pill-bugs, are usually found ; or as excrement of 
grazing animals, in which certain molds, certain dipter- 
ous and scarabaeid larvae, etc., regularly occur, irrespect- 
ive of surrounding conditions; (4) invaders from near- 
by associations; (5) ruderal and introduced species; and 
possibly one or two other groups. The second and third 
groups may be called the irregular element; the fourth 
and fifth may be known as the derived element. While 
these groups make a formidable list, their representa- 
tives constitute usually a very small proportion of the 
organisms of the association. The other organisms, and 
some of these, follow habitat-differences, as represented 
in different associations, very closely. 

Since hardly any two species are identical in habitat- 
relations, geographic and even local variation must be 
looked for, but since many species resemble each other 
more or less closely in general ecological relations, there 
come to be recognized certain ecological groups of spe- 
cies, each characterized by a general type of growth-form 
in plants, or by a general kind of mores in animals, and 



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440 THE AMEBIC AN NATURALIST [Vol. XLVIII 

these groups may be considered to be small or large, 
according as we emphasize minor differences or general 
likenesses. 

Now within any limited region (let us postulate first 
an area removed from the influence of an adjoining prov- 
ince) there are only a limited number of ecological 
groups, of growth-forms of plants, and of mores among 
animals, each group represented by a limited collection 
of species. Each habitat within this restricted area will 
be characterized by definite physical conditions, and with 
these will be correlated certain growth-forms of plants 
and certain mores of animals, each represented by as 
many of the species as can migrate into and survive 
within the area, as determined first by capabilities of 
migration and by habitat-selection, and second by inter- 
relation of species and of individuals. It follows that 
physical complexes which are alike will become populated 
with similar complexes of ecological groups, represented 
by similar collections of plant and animal species, and 
that unlike physical areas will be occupied by different 
combinations of ecological groups, and will be composed 
of different species. Two areas within this region which 
have similar physical conditions and similar plant 
growths will be expected to have a large number of ani- 
mal species in common, although direct relations between 
species of animals and species of plants obtain only 
rarely (between comparatively few associated plant-and- 
animal pairs). It is to be noted that species composition 
of the animal assemblage varies proportionately no more 
widely than does that of the plant assemblage. 

No terrestrial continental region is sufficiently isolated 
to be free from influence of surrounding areas, and since 
the influences are different from different directions, and 
since there is continual change of physical conditions, and 
of range and abundance of plant and animal species, 
there must be more or less local and geographic varia- 
tion of species composition within similar but separated 
habitats. Geographic variation is wider with distance. 



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J^p. 571] 



TEBRESTBIAL ASSOCIATIONS 



441 



because the geographic and physiographic complexes 
vary geographically, as well as the entire collection of 
plant and animal species which may invade the habitat. 
Within the area of the climatic province, however, or at 
least within the area of a subregion of the province, 
climatic, physiographic and biotic complexes are likely 
to be relatively constant, that is, likenesses of two areas 
are likely to be greater and more striking than differ- 
ences. Within the province or. subregion, therefore, it 
is to be expected that species composition of association 
of closely similar habitats will be relatively constant 
Particular plant and animal assemblages will be found 
together, both associated with a particular habitat. Field 
observation bears out these expectations. 

Conditions within the transition zone between two 
climatic regions or provinces are much more complex 
than in an area in the middle of a sub-region or province ; 
climatic and physiographic conditions vary to wider 
extremes and are less stable ; the total number of species 
near enough at hand to invade a given habitat is much 
greater. Mixed associations, often transitional as re- 
gards physical conditions, are composed of representa- 
tives of both provinces. Animals of a particular associa- 
tion of one province, may be found with plants of a 
similar or equivalent association of the other province. 
When three geographic elements are represented, as at 
the southern end of Lake Michigan (cf. C, and Vestal, 
1914a), the complication of conditions is extreme. Even 
here, on the dry sand of old lake beaches, fairly typical 
representations of sand prairie can be seen ; and though 
such habitats are shared with deciduous forest associa- 
tions, and with associations of the northeastern coniferous 
forest province, and with mixed associations, the bunch- 
grass growth can still be recognized in dry shifting sterile 
sand, with bunch grass plant species, and bunch-grass 
animal species. The tendency towards uniformity of 
association of plant and animal assemblages is even here 
to be made out. 



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442 THE AMEBIC AN NATURALIST [Vol. XLVHI 

If the foregoing considerations relating to relations 
between plant and animal communities are correct, the 
thesis mentioned at the beginning of part V would seem 
to be justified, though the evidence is far from complete. 
Plant and animal assemblages are mutually interdepend- 
ent; the plant assemblage dominates in established 
associations. Plant and animal assemblages correspond 
in geographic distribution, in distribution into commu- 
nities, and in more detailed distribution within the 
habitat. They are made up of ecologically similar groups 
correlated with the same physical conditions or with 
each other. Though there are few direct relations be- 
tween particular species of plants and animals, it so 
happens that within any restricted region, particular 
collections of animal species come into regular associa- 
tion with particular collections of plant species, the spe- 
cies composition within the habitat exhibiting a greater 
or less degree of uniformity, except for minor irregular 
and derived elements. The more restricted, or uniform 
in biological conditions, this region is, the greater the 
uniformity of the collection of species. Climatic and ex- 
tensive associations, and established associations, show a 
greater degree of uniformity than local or primitive 
associations. 

VI. SUMMARY AND CONCLUSIONS 

The discussion is based principally upon the writer's 
study of prairie associations, the bunch-grass associa- 
tion of sand prairie in Illinois being chiefly used for illus- 
tration. Internal activities of the association are a com- 
plex of activities of all the organisms. Environmental 
influences are of three classes, physical, plant and animal. 
The characters of plants and animals are interpreted in 
their relation to these influences. Characters of plants 
may be classed as structural, physiological, biographical 
and numerical. Animals have, in addition, behavior or 
psychological characters. These groups of characters 
are intimately related, one to another. The relations of 
the animal to its animal-environment are of two kinds, 



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No. 571] TERRESTRIAL ASSOCIATIONS 443 

social and antagonistic, the latter relations being with 
food-species, competitors and enemies. Correlations of 
the various kinds of characters with relations involving 
food, competition and enemies, are given. According to 
its ecological constitntion, each organism finds a status 
in the association, the whole being a self-contained and 
self -regulating system of activities. 

Dependencies within the association are concerned 
mainly with sources and interchange of material and 
energy. Dominant plants (the most influential species) 
are those most intimately correlated with physical en- 
vironment, as indicated by aggressiveness, abundance, 
frequence, size, etc. Domiaant animals are most numer- 
ous among phytophagous forms. Dominance in an ani- 
mal species includes dependence of other animals upon it 
(for food) plus the ability to thrive in spite of the drain 
upon its numbers. The degree of specialization of be- 
havior is a convenient index of the relative influence of 
animals in the association. The dominant animals are 
moderately specialized, and carry on the ordinary work 
of the association. The highly specialized animals make 
use of space otherwise unoccupied, and food material not 
available to other species, or not taken by other forms. 
Least highly specialized animals act as a check upon 
undue departure from biotic equilibrium. 

The association may be divided into minor groups of 
organisms, both in space and in time. Space-division is 
vertical, resulting in strata, and horizontal, resulting in 
sub-habitats of greater or less magnitude. The strata 
and sub-habitats present a larger or smaller degree of 
discontinuity and of internal variability. Time-distribu- 
tion is diurnal, seasonal and annual. There are also 
time- variations produced by variability of weather condi- 
tions and by oscUlatory disturbances. 

The relations between plant and animal assemblages 
have long been known, in a general way, to be intimate. 
Plants and animals agree in similar response to common 
environmental influence, and in types of geographic dis- 



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444 THE AMERICAN NATURALIST [Vol. XLVm 

tribution. Upon investigation, it begins to appear that 
plant and animal assemblages are coextensive parts of a 
biotic association, composed of both plants and animals, 
and this association as a whole constitutes the real ter- 
restrial community of living organisms. Plant and ani- 
mal assemblages are mutually interdependent ; the plant 
assemblage dominates in established associations. Plant 
and animal assemblages correspond in geographic dis- 
tribution, in distribution into communities, and in more 
detailed distribution within the habitat. They are made 
up of ecologically similar groups correlated with the 
same physical conditions or with each other. Though 
there are few direct relations between particular species 
of plants and animals, it so happens that within any 
restricted region, particular collections of animal species • 
come into regular association with particular collections 
of plant species, the species composition within the habi- 
tat exhibiting a greater or less degree of uniformity, 
except for minor irregular or derived elements. The 
more restricted in area, or uniform in biological condi- 
tions, this region is, the greater uniformity of the collec- 
tion of species. Climatic and extensive associations show 
a higher degree of uniformity than local or primitive 
associations. 

VII. REFERENCES 

r> Special Befereiices 

(A) Shelf ord, V. E. 

19116. Physiological Animal Geography. Jour, Morph., 22: 551- 
618. 






1912a. Ecological Succession. IV. Vegetation and the Control 
of Land Animal Communities. Biol, BuU., 23: 59-99. 



1913. Animal Communities in Temperate America. Geogr. Soc. 

of Chicago, Bull. No. 5, p. 362. Chicago. 
(D) Vestal, A. G. 

1913a. Local Distribution of Grasshoppers in Relation to Plant 

Associations. Biol. Bull, 25: 141-180. 



(E) 



1913&. An Associational Study of Illinois Sand Prairie. Bull. 

III. State Lab. Nat, Hist., 10: 1-96. 
Other Articles Cited 
Adams, C. C. 

1913. Guide to the Study of Animal Ecology, p. 183. New York. 



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No. 571] TEBBESTBIAL ASSOCIATIONS 445 

Craig, W. 

1908. North Dakota Life: Plant, Animal, and Human. Bull Am. 

Geogr, Soc, 40: 321-332, 401-415. 
Ellis, M. M. 

1914. Fiahes of Colorado. Univ, CoXO. Studies, 11 : 1-136. 
Forbes, S. A. 

1880. On Some Interactions of Organisms. Bull. III. State Lab. Nat. 

Hist., Vol. 1, No. 3, pp. 3-17. 
1883. The Begulative Action of Birds upon Insect Oscillations. Bull. 

m. State Lab. Nat. His., Vol. 1, No. 6, pp. 3-32. 
1887. The Lake as a Microcosm. Beprint from Bull. Sci. Assoc, of 
Peoria, III., pp. 1-15. 

1909. The General Entomological Ecology of the Indian Com Plant. 

Am. Nat., 43: 286-301. 
Gates, F. C. 

1912. The Vegetation of the Beach Area in Northeastern Illinois and 

Southeastern Wisconsin. Bull. HI. State Lab. Nat. Hist., 9: 

255-372. 
Gleason, H. A. 

1910. The Vegetation of the Inland Sand Deposits of Dlinois. Bull. 

Ill State Lab. Nat. Hist., 9: 23-174. 
Hart, C. A., and Gleason, H. A. 

1907. On the Biology of the Sand Areas of IlHnois. Bull III State 

Lab. Nat. Hist., 7: 137-272. 
Nelson, E. W. 

1909. The Babbits of North America. Bur. BioL Surv., U. S. Dept. 
Agr., N. Am. Fauna No. 29, pp. 314. 
Pound, R, and Clements, F. E. 

1898. The Vegetation Eegions of the Prairie Province. Bot. Gas., 25: 
381-394. 
Buthven, A. G. 

1908. The Faunal Affinities of the Prairie Begion of Central North 

America. Am. Nat., 42: 388-393. 
Schimper, A. F. W. 

1903. Plant Geography upon a Physiological Basis. Oxford. 
Shelford, V. E. 

1911a. Ecological Succession. I. Stream Fishes and the Method of 

Physiographic Analysis. Biol Bull, 21: 9-35. 
1912&. Ecological Succession. V. Aspects of Physiological Classifi- 
cation. Biol Bull, 23: 331-370. 
Vestal, A. G. 

1914(1, The Status of Prairie Associations in the Southern Beach Areas 

of Lake Michigan. Jour. Ecology. (In press.) 
1914. Prairie Vegetation of a Mountain-front Area in Colorado. Bot. 
Gae. (In press.) 
Transeau, E. N. 

1903. On the Geographic Distribution and Ecological Eelation of Bog 

Plant Societies. Bot. Gajg., 36 : 401 et seq. 
1905. Forest Centers of Eastern America. Am. Nat., 39: 875-889. 



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SHOETEE AETICLES AND DISCUSSION 

ANOTHER HYPOTHESIS TO ACCOUNT FOR DR. 
SWINGLE'S EXPERIMENTS WITH CITRUS 

The results of the cross-breeding experiments with forms of 
Citrus by Walter Swingle have given rise to quite a number of 
different hypotheses, to account for the facts observed. 

The facts are simply these. All the different forms of Citrus 
used in the experiments, Citrus trifoliata, th€ lemon, orange and 
other citrous fruits have, so far, proved to reproduce their own 
type through seed. 

Nevertheless, the plants raised from one single cross are ex- 
ceedingly different among themselves. And yet, all these new 
forms, for so far as tested, have proved truly to reproduce their 
own kind only, if sown. 

The theories offered to account for these facts are rather com- 
plex. So far, we have not seen the simple hypothesis which we 
want to add to the others. 

The fact, that the Fi from almost every cross between types of 
Citrus is multiform, can only be accounted for on the assumption, 
that the parent plants are impure (heterozygous) for a number 
of genes. The difficult question is this : how can a tree, impure 
for a number of genes, produce seed which always only repro- 
duces the type? We know, that if a plant reproduces itself 
by an asexual method, all its daughter plants are pure for 
those genes in respect to which it was pure, impure for those 
genes for which it was impure. Is it possible that in these 
trees the seeds normally produced are not derived from a union 
between two normal gametes? In Citrus, with its adventitious 
embryos, this is very well possible. If the forms of Citrus used 
by Dr. Swingle are self-sterile, the seeds normally produced by 
these trees, are not produced by the union of two gametes, but 
as buds, asexually. 

This hypothesis, that the Citrus used are self -sterile,- and that 
the seeds normally produced, are produced asexually, fully ac- 
counts for all the facts. All the daughter plants from un- 
crossed seeds are genotypically identical with the mother plant, 
as in all clones. On poUenization by another tree, normal seeds 
are produced, each the result of the union of two real gametes. 

446 



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No. 571] SHOETEB ARTICLES AND DISCUSSION 447 

These seeds contain different combinations of the genes, for 
which the parent plants are impure, as normally. The Fj gener- 
ation for this reason becomes as diverse as such generations 
always are, if the parents are impure for numerous genes. 

But these daughter plants^ although impure for a number of 
genes, can, because of their self -sterility, in their turn only pro- 
duce seed asexually and therefore their offspring will be like 
themselves. 

It should not be diflBcult to test our hypothesis. It seems 
easier to find out, whether the seeds produced without crossing in 
jCitrus contain the embryo formed by fertilization of the em- 
bryo sac, or embryos formed adventitiously by the adjacent tis- 
sue, than to test any of the other theories, which assume a pecul- 
iar behavior of the chromosomes. 

Our hypothesis, that a variable Fj, of only true-breeding 
plants (from the union of two true-breeding forms), results 
from habitual self-sterility and asexual production of seed, with 
real fertilization in the case of a cross taking place, not only 
accounts for the facts found by Swingle, but also for those found 
by Kosen with Erophila vema. These facts were somewhat dif- 
ferent. The Fi plants were all identical, and somewhat inter- 
mediate. They gave rise to a variable Fj generation of which 
all the plants bred true to their type. These facts can be ex- 
plained on the assumption, that Erophila vema is self-sterile, 
and that, in the absence of cross-fertilization, unfertilized egg- 
cells develop parthenogenetically. Such F^ plants, which are 
impure for a number of genes, should therefore produce as many 
different kinds of F^ plants, as there are female gametes pro- 
duced, and in the same proportions. In the case of such a plant 
being impure for two genes, we should expect it to produce 
plants of the four different types, not in the usual proportion of 
9:3:3:1, but in equal proportions, 1:1:1:1. The F^ plants 
from such seed could only be pure for all the genes present. 

It would be possible in Erophila vema to find out whether F^ 
plants, impure for two genes, produced daughter plants of the 
four kinds, AB, Ab, aB, and ah, in the proportion of 9 : 3 : 3 : 1, 
or in proportion 1:1:1:1, and thus to test our hypothesis. 

To find out, whether it is possible, that aC plant, impure for a 
number of genes, produces a variable F2 generation of only 
completely homozygous plants, we have begun a series of experi- 
ments with squashes. Some hybrid plants have not produced a 



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448 THE AMERICAN NATURALIST [Vol. XLVIU 

single fruit from carefully sealed female buds, others have given 
plenty of empty fruit, but some hybrids have produced several 
fruits, full of viable seed. If this seed is formed by the par- 
thenogenetic development of unfertilized normal egg-oells, as 
we have reason to believe, we expect to raise a variable P, gene- 
ration of exclusively homozygous plants. If these seeds have 
developed by apogamy, or any other asexual process, we expect 
to obtain a second generation consisting exclusively of plants 
like the original hybrids. Thus we will have a non-cytological 
test to decide between apogamy and true parthenogenesis. 

A. C. Hagedooen, 

A. L. Hagedoobn 

BussuM, Holland, 
March 18, 1914 



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A Journal for the statistical study of biological problems, appearing about four times a year. A volume 
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A great Tsriety d questions conoetning gsnwal anivsnity administration an dealt with in an original and 
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Thesa quotations and essmples are taken from Professor Cattell's inf osmed and thoroogh dlseosrion of the 
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The American Naturalist 

A MoBllilr Joonial. MtaUialied in 1867, D«TOted to the Adrancemeiit ol the BiologiMi Sriiiim 
with Special Raf ereaco to tfao Faetors ol Orvanic EvolotioM and HaraditF 



CONTENTS OF THE JANUARY NUMBER 

A Genetic Analyiii of the Changes produced by 
Selection in Sxperlments with Tobacco. Pro- 
fessor B. M. Bast and H. E. Hayes. 

Gynandiomorphous Ants, described during the De- 
cade, 1903-1918. Professor WiUiam Morton 
Wheeler. 

Shorter Articles and Discussion : On the Results of 
Inbreeding a Mendelian Population— A Correc- 
tion and Extension of Preyious Conclusions. 
Dr. Baymond Pearl— Isolation and Selection 
alUed in Principle. Dr. John T. Gnlick. 



CONTENTS OF THE FEBRUARY NUMBER 

Some New Varieties of Bats and Gaine«-idgs and ttieir 
Belations to Problems of Color Inheritaaee. Pro- 
fessor W. B. Castle. 

•• Dominant" and " Kecess.ye" Spotting in lOce. C. 
c Little. 

On Difler^tialMortaUty with respect to Seed Weight 

occurring in Field Coltures of Pisum sattTom. 

Dr. J. Arthur Harris. 
The InheritaBce of a Beeorring Somatic Varlatloa 

In Variegated Bars of Maise. ProfeMor B. A. 

Bmerson. 

Restoration of Edaphosftunis erndger Cope. Pro. 

fessor B. a Case. 
Shorter Articles and Discussion : Humiditj— a 

Neglected Factor in BnTironmentftl Work. Dc 

Ftank B. Luts. 



CONTENTS OF THE MARCH NUMBER 

The Effect of Extent of Diitrlbntlon on Speeiation. 

Asa C. Chandler. 
Biology of the Thysanoptera. Dr. A. Franklin Shull. 
Shorter Articles and Correspondence : The Endemic 

Mammals of the British Isles. Professor T. D. A. 

OockerelL 

Notes and Literature : Swingle on Variation in Fi 
Citrus Hybrids and the Theory of Zygotaxis. 
Dr. Orland E. White. 



CONTENTS OF THE APRIL NUMBER 

The Origin of X Capsella Bursa pastoris araehnoideab 
Dr. Henri Hus. 

Biology of the Thysanoptera. n. Jh, A. Fraskltn 
Shull. 

Shorter Articles and Discussion: Barriers as to Dis- 
tribution as regards Birds and Mammals. Joseph 
Grinnell. Yellow Varieties ot Bats. ProflBSSQr 
W. E. Castle. 

Notes and Literature : Heredity and the Tnfhieiioe 
of Monarchs. V. L. K. 



CONTENTS OF THE MAY NUMBER 

Betoparasitesof Mammals. Professor Vernon Lyman 

Kellogg. 
Begeneration, Variation and Correlation in Thyone. 

Professor John W. Scott. 
Shorter Articles and Discussion : Terms relating to 

Generic Types. Dr. O.F.Cook. 
Notes and Literature: Linkage in the Silkworm 

Moth. A. H. Sturterant. Nabours^s Breeding 

BxperlmentB with Grasshoppers. John a Dexter. 



CONTENTS OF THE JUNE NUMBER 

Species-bailding by Hybiidintion and Matati<m. Pro- 
fessor John H. Gerould. 

Heredity of Bristles in the Commtm Greenbottle Fly— 
A Study of Factors goTemingDistiibatioiL FhineM 
W. Whiting. 

Physiological Correlations and Climatic ReaotionB in 
Alfalfa Breeding. Geo. F. Freeman. 

Taxonomy and Erolution. By X 

Shorter Articles and Diacosrion: NabonnPs QnMS- 
hoppera, Multiple Allelomorphism, Tan^«e and 
if^fiiAiiing Terminologies in Genettos. 
W. ELCsstle. 



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TOL. ZLVm, VO. 672 ATTOTTST, 1914 



THE 

AMERICAN 
NATURALIST 



A HOHTHLT JOmUTAL 

Itofotad to fhe Advancemdnt of fhe Biolog^eal Soieii06f wift 

Special Beferenoe to fhe Paotors of Erolutiom 

COVTBVTS 



Pag9 * 1 

I. Koltlple AlUlomorpha In Mloe. Profeisor T. H. Mob0an - - - - 449 J 

IL Tldrteen Tears of Wheat 8«leotloii. T. B. Hutohbson - - - - .459 ; 

m. Pattern Derelopment In iraininala and Blrda. Glotbb M. Allxn - - 467 
IV. The Meadow Jumping Honae. Dr. H. L. Babcook ..... 430 

y. Shorter Artlelea and IMienaslon : Studies on Inbreeding. Dr. Batmomd J 

Pbarl. Parallel Mntations in (Enothera biennis L. Dr. J. STOMPS, Dr. ' i 

Bbablby M. Davis. The Theoretical Distinction between Multiple Allelo- ; 

morphs and dose Linkage. ProfSsssor T. H. Mobgan, Professor W. E. { 

Castlb -------------- 491 I 

VI. Motes and Literature: Biometrics. Dr. Baymond Pbabl. A New Mode ef \ 

Segregation in Gregory's Tetraploid Primulas. HBBMAKif J. Mullbb - 500 



THE BODSNOE PBEBB 

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The American Naturalist 

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•oat to the Editor of THE AMERICAN NATURALI8T, fiarriooa-oa-Hadooa. Now York. 

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Farthor roprlato will bo oappllod at coot. 

8aboorlptloao aad advortlooaioato oboald bo ooat to tho pabllohors. Tho 
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FOR SALE 

ARCTIC, ICELAND and GREENLAND 

BIRDS' SKINS, 

Well Prepared Low Prices 

Particulars of 

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a aet of BIRDS OF AMERICA by J. J. Auddxn. 
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P. C. HARRIS, 
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For Sale Entire 

An important oollection of Indian Birds' 
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bellied Minivet (Pericrocotus erythro- 
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Particidars and full list may be had 
from 

W. F. H. ROSENBERG 

57 Haveratock HiU London, N. W. 



Marine Biological Laboratory 

Wooda Hole, Mass. 



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Comaes of laboratory 

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THE 

AMERICAN NATURALIST 

Vol. XLVIII August, 19U No. 572 

MULTIPLE ALLELOMORPHS IN MICE 

PROFESSOR T. H. MORGAN 
Columbia University 

Some breeding experiments with mice that I have been 
carrying on during the last two years have shown that 
yellow, gray gray-belly, gray white-belly and black are 
allelomorphs. To this series a fifth allelomorph may pos- 
sibly be added which for the present naay be called new 
gray. This quadruple (or quintuple) system of allelo- 
morphs fulfils the conditions of a multiple series in that 
only two of the allelomorphs can exist at the same time 
in any individual. In other words, a mouse may be pure 
for any of these genes (except for yellow, in which the 
pure form is not viable), or a mouse may be heterozygous 
in any two of the genes, but never in more than two. 
The evidence that establishes this series of allelomorphs 
may be briefly stated as follows : 

In 1911, I pointed out that if yellow mice (producing 
yellow and chocolates) are bred to agoutis (grays), and 
their yellow offspring mated, they should produce not 
only yellow and agoutis (as they did) but some choco- 
lates (or blacks) also; but no chocolates appeared. I 
stated that the results obtained were explicable if yellow 
and agouti are allelomorphs.^ 

1 The discussion in the same paper of the presence of chocolate yellow and 
black bars in the ticked hair in relation to the occurrence of chocolate, yel- 
low and black color in domesticated races may only confuse the ontogenetic 
production of characters with the gametic inheritance of factors. The 

449 



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460 THE AMEBIC AN NATURALIST [Vol. XLVl. 

Sturtevant (1912) showed that the results are also 
consistent with the hypothesis that there is close or com- 
plete linkage (genetic coupling) between yellow and 
agouti. In principle this is the same as saying that when 
yellow and agouti enter from different sides (mother and 
father) they separate in gametogenesis, or in other words 
they '* repel '' each other and behave, as I said, like 
allelomorphs. 

The numerical results would be the same whether 
yellow and agouti arei treated as though completely 
linked or whether they are? treated as allelomorphic. 
What I had vaguely seen in my 1911 paper was clearly 
explained in the following year by Sturtevant 's treat- 
ment of the same data, to which he added that of Little 
and Miss Durham. 

Sturtevant showed, from an analysis of Miss Dur- 
ham's results, in which she used ordinary gray (gray 
'* gray-belly '0 niice, that her results are consistent with 
the hypothesis of absolute linkage, or, on my interpre- 
tation, with the hypothesis of allelomorphism. Sturte- 
vant 's conclusions were promptly contradicted by C. C. 
Little on the evidence furnished by some of his earlier 
experiments, in which he obtained yellow, grays and 
black (or chocolates) in offspring from yellow to black 
(or chocolates). Such a result would be inconsistent 
with Sturtevant's hypothesis. Little also appealed to 
certain experiments of Miss Durham, in which, he stated, 
results like his own are given. Since Little has been 
unable to get again his former results, but has obtained 
evidence in favor of Sturtevant 's view, and since it is 
clear that he misunderstood Miss Durham's evidence, 
his contradiction ceases to have any weight. 

factorial hypothesis relates to those differentials that serve to separate 
different types in inheritance and is not concerned with the problem as to 
how those differentials produce their effects. Breeding experiments show 
that gray differs from black by one differential, from yellow by another, and 
from cinnamon by a third. So far as Mendelian segregation of these dif- 
ferential genes is concerned it is of no consequence that the gray hair is 
made up of a black, a yellow, and a chocolate band. 



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No. 572] 



MULTIPLE ALLELOMORPHS 



451 



After the publication of my own and of Sturtevant^B 
paper I set to work to obtain crucial evidence in favor 
of, or opposed to, the view that yellow and gray are 
allelomorphic. Little, also, it appears, has carried out 
some new experiments which he has recently published, 
with the results just stated. My own data have been 
ready for some time> but I have withheld them in order to 
get a sufficient body of evidence to make the case con- 
vincing, especially in the light of the possibility that the 
crossing over might occur in one sex and not in the other. 
For, if no crossing over occurred in the male, there 
might be crossing over in the other sex, which would not 
reveal itself unless the experiments were deliberately 
planned so that both sexes are tested. This consideration 
seems to have been overlooked by Little, for he has 
omitted in his confirmatory paper to give the sexes of the 
animals used. Without a knowledge of this relation even 
his confirmation fails to confirm (as he supposes) the 
view that he formerly combated. 

Since Miss Durham worked with common gray and I 
with gray white-belly, and both are ** repelled ^^ by yellow, 
i. e., both are allelomorphs of yellow, it follows that these 
two grays are also allelomorphic to each other. 

The evidence that black belongs to the same series of 
allelomorphs is obtained in the following way : If a given 
yellow is mated to black, and yellow and gray offspring 
are obtained, and if then the yellow offspring are mated 
to black again and now give yellow and black only, the 
proof is furnished; for in the first mating yellow and 
agouti have repelled each other, and the yellow-bearing 
gametes have united with the black gametes of the other 
sex to give the yellow offspring. The second mating 
shows that black is now repelled in turn by yellow and is 
tiieref ore allelomorphic. 

This may be illustrated in the following way: Let 
B^ = yellow, b = black and B = gray. These three 
factors may be treated as allelomorphs, then: 



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452 THE AMERICAN NATURALIST [Vol. XL VIII 

Y ellow B^B by black bh, 

Gametes of Pj yellow B^-B. 
Gametes of Pi black b-b. 
p B ''6= yellow. 
* Bb =gray. 



Gametes of F^ yellow B''-6. 
Gametes of pure black b-b. 

^ 5*'6 = yellow. 

^'bb = black. 

But if yellow and black and gray are not allelomorphic 
the same matings should give the following results : 

¥' = yellow, y' = not yellow, b = black. B = * * gi av ' ' ( not black ) . 
Yellow YY BB by black l/ybb^^ 
Gametes ofP, yellow Y'B-i/B, 
Gametes of Pi pure black y'b-y'b. 
p Y'B 3/'6=7SIow. 

^ y'B y'b=zgT2L y. 

Gametes of Fi yellow Y'b-Y'B-y'b-y'B. 
Gametes of pure black y'b-y'b. 
Y'¥ ~y'b = yellow^ 
„ Y'B y'b= yellow. 
^» y'6 i/'6 = black. 
y'B i/'6=:gray. 

On the second assumption yellow, gray and black 
should appear in the back cross. The former and not the 
latter view is therefore consistent with the actual results. 

The Symbols Employed 
It is, of course, a matter of secondary importance what 
system of symbols is followed. The requirements are 
simplicity, consistency and suggestiveness, but one can 
not always arrange to have all three at the same time. 
The simplest scheme, for a system of allelomorphs like 
these, would be to have some common letter to indicate 
their relation and an exponent to suggest the different 
characters for which each stands. If we take the symbol 
b (black) for the common letter, and use capitals for 
dominance, the allelomorphs will be: 

b = black. 
B^= gray gray belly. 
5"'=: gray white belly. 
B^ = yellow. 

If one preferred to take Y (yellow) as the common letter 
the series would be y'^, y'^, y'^, Z'; or, if one preferred 



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No. 572] MULTIPLE ALLELOMORPHS 453 

to take G (gray), as the common letter, the series would 
be g^, g^y G, g^\ On the whole the first series seems to 
me somewhat preferable. 

The factor for cinnamon is entirely independent in 
heredity of the preceding series of allelomorphs. This 
factor may be represented by ci and its normal allelo- 
morph by Ci. The formula for the wild gray would then 
be Ci Ci, and that for cinnamon would be ci ci. Black 
would be h b, and the double recessive cinnamon black 
(or chocolate) would be bb ci ci. Chocolate is one of the 
commonest types of domesticated mice and since I have 
used it very extensively in my matings, its relation to the 
other types may be further stated. It is known that if 
chocolate is bred to wild gray, and if the gray offspring 
that are obtained are then inbred, they give, in Fo, the 
following classes: 9 wild gray, 3 cinnamon, 3 black, 1 
chocolate. 

It is clear that chocolate is the double recessive type. 
Of the two genes, that differentiate chocolate from wild 
gray, chocolate has one in common with cinnamon and 
the other with black. In other words, chocolate is cin- 
namon black, and technically should receive this name. 

The Experimental Evtoence 
Is There a Separate Factor for White-belly? 
The first series of experiments was made in order to 
determine whether the peculiarity of white-belly, shown 
by the wild race of white-bellied grays, is due to a factor 
that may be separated from the gray white-bellied mice, 
or whether it is completely linked to gray (or allelo- 
morphic to it). As wild gray house mice offer some 
drawbacks in breeding work, I used cinnamon blacks 
(chocolates). Gray white-bellied mice were bred to 

2 It is not possible to make a system of allelomorphs (in which the 
"compounds'^ are serially epistate to each other) consistent entirely with 
the system of nomenclature that I have suggested for the usual cases in 
which mutant allelomorphs are contrasted with the normal allelomorphs of 
the wild (or supposed original) type. 



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464 



THE AMERICAN NATURALIST [Vol. XLVHI 



chocolates.^ The gray white-bellied offspring were se- 
lected and these were bred again to chocolate. The cross, 
in regard to sex, was made both ways. If there is an 
independent factor for white-belly that can separate from 
the factor for gray gray-belly, then some gray gray- 
bellied mice should appear. None were obtained, as the 
following table shows. We must conclude either that 
there is one factor that gives the gray white-bellied coat, 
or else that the postulated factor for white-belly is so 
closely linked to the gray factor that it has not sepa- 
rated once in 100 times. Therefore unless such a sepa- 
ration occurs it is simpler to assume one factor for gray 
white-belly that is allelomorphic to black and to gray 
gray-belly, etc. 

TABLE I 



Mating 


Gray or Cinoa- 
mon White- 
belly 


Black Chocolate White 

1 




cf 


9 


cf 


9 1 cf 


9 d^ 


9 


Gwb 9 by Ch cf . . . . 

Ch 9 by Gwb cf 

Totals 


7 
2 
9 


21 
14 
35 


2 
3 
5 


9 
10 
19 


5 

4 
9 


11 3 
10 1 
21 3 


1 
1 













Taking both crosses together, there are 44 grays to 54 
blacks and chocolates, which approximate at least to 
expectation. To these numbers I may add the follow- 
ing data taken from similar experiments made for other 
purposes in which one parent was, as before, gray white- 
belly. 

Gray-white Belly. Black or Chocolate, 

c? 9 c? S 

17 25 20 20 

Presumably, therefore, the results may be treated as 
though a single gene for gray white-belly exists. It will 
be observed that the experiment has been made in two 
ways, for at the time I was aware of the possibility that 
crossing over, if it occured, might be limited to one sex. 

• At the time when the experiment was made all the gray white-bellied 
mice were heterozygous for black and for agouti (including some with the 
factor for cinnamon). 



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No. 572] MULTIPLE ALLELOMORPHS 455 

We are justified, therefore, in treating gray white-belly 
as an allelomorph of gray gray-belly, the former domi- 
nating. If crossing over should occur, it might perhaps 
only be realized in the gray or cinnamon mice, since it is 
possible that the ticked condition of the hair (that is, 
common to gray and to cinnamon) is necessary to realize 
this condition. The expected crossover that would be 
observed would be gray gray-belly mice. The contrary 
class would then be black or chocolate mice that carry 
the factor for white-belly that might or might not show 
the influence of the supposedly separable factor. 

My white-bellied stock of mice had been killed after 
my earlier results had been published, but Mr. B. B. 
Horton had kept some of my original stock alive, and 
from him I obtained a few of these mice in 1912 to carry 
on the above experiments. 

An extraordinary sex ratio appears in the next to the 
last table, where there were 26 males to 76 females, ap- 
proximately 1:3. The mice were entered when about 
three weeks old. The sex was noted, but no special atten- 
tion given to the determination. There is some chance 
of mistaking the sex of young mice, but one familiar 
with these animals can determine with certainty the 
sex at three weeks if sufl5cient care is taken. I have no 
reason to suppose that I made such errors which would 
have to be frequent to give these results. If taken, then, 
at their face value, the data seem to show that there is a 
sex-linked lethal gene present here. It is not linked to 
any of the factors involved, and this is not expected, 
since neither black nor agouti is sex-linked. If further 
work confirms this conclusion (and I hold it as a provi- 
sional conclusion until it can be further studied) we have 
here the first evidence of a sex-linked gene in mice. A 
sex-linked lethal should give a sex ratio of 1(?:2$. 

The Allelomorphism of Yellow, Gray and Black 
The allelomorphism or '* repulsion '* of yellow and 
agouti (gray) may be tested in various ways. One of the 



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456 



THE AMEBIC AN NATURALIST [Vol. XLVIII 



simplest tests is the following: Yellows were bred to 
chocolates. The combination gave yellow and agouti off- 
spring, when certain yellows are used, and yellow and 
chocolate offspring when other yellows are used. Mixed 
litters of yellow, agouti and chocolate do not appear. 
Now when yellow and agouti appear in a given litter (as 
above) the yellow parent must have carried agouti. If 
her yellow gene ** repels'' the agouti gene, then none of 
the yellow daughters should contain agouti genes, con- 
sequently if such yellows are next bred to chocolate the 
offspring should be only yellow and chocolate (or black) 
and never yellow and agouti. This, in fact, is what my 
experiments have shown. In the two following tables the 
results of crossing yellows by chocolates are given by 
litters. The yellows that were used at first were for the 
most part heterozygous for gray white-belly, hence in 
the. earlier litters yellows and grays were generally ob- 
tained. The yellow offspring of these earlier litters were 
for the most part used in the later experiments, hence 
the later litters are made up of yellows and chocolates. 
The records (not given here) showed in every case that 
yellow mice from litters of yellow and gray gave, when 
bred to chocolate, only yellows and chocolates. 



TABLE II 

Yellow ^ by Chocolate $ 

Litters 



Yellow 


1 


11 

2 . 

. 1 


4 


3 13 24 


4 Q^^^^'s 


5 4!3 5 7!2l2'2 2 

34|. . .|. .1. . 


34 3 2412 2 

.i. .j. 4 . .1. 


?| 


Gray 




5 


422 . 
! ! ! 2 


4 


4 4 55 



4'. 
.1. 




Chocolate 

White 


i 


. .2343.33 

. .I.l.i.l. . .1. 


. 2 3.2 . 34 2 


3 



TABLE III 

Yellow $ by Chocolate c? 

Litters 



Yellow.... 414 

Gray 5 ..2 

Chocolate 


4|3 

5!2 


4 
1 


4'2'4 
12.. 
. . . . 1 


1 4 88 
3 5 13 


1 

1 


2I2 8 
.. .. 3 
22 .. 


3 
1 


2 


2 

'2 


1 
3 


1 
4 


4 
2 


3 
3 


4 
1 


Black 1. . . . 












? 


White 1 . . . . 






i 






1 2!.. 







































* Probably two litters combined. 



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No. 572] MULTIPLE ALLELOMORPHS 457 

TABLE IV 

Summary op Litters 

Yellow and Gray Yellow and Chocolate 

Yel. Gray Yel. Choc. 

101 78 70 67 

The experiment is not demonstrative, however, unless 
both the yellow daughters and sons are bred to chocolate, 
for it might be that yellow and agouti are linked and 
crossing over might occur in one sex and not in the other 
sex. For instance, if we start again with yellow by choc- 
olate, then if their yellow offspring contain agouti linked 
to yellow that does not cross over in one sex, let us say in 
the males, it follows that a yellow male bred to chocolate 
would give only yellows and chocolates, for the agouti 
gene would go with the yellow. Therefore, both sexes 
must be tested. This essential element in the proof has 
been overlooked by Little, for he fails to state whether his 
test experiments were made with both sexes. In my 
main experiments I have used yellow sons only, and the 
tables are based on those data, but in a few cases I have 
mated the yellow daughters (whose brothers were agouti) 
also to chocolate and have found that these females give 
only yellows and chocolates, which shows for both sexes 
that no crossing over of yellow and agouti occurs. 

A specific case will illustrate this point. A yellow 
male was bred to a chocolate female and gave 5 yellow 
and 7 gray offspring in two litters. One of the yellow 
daughters was bred to chocolate and in four litters pro- 
duced 11 yellows and 9 chocolates. A yellow grand- 
daughter gave 9 yellows, 7 chocolates and 4 whites. 

A yellow female bred to chocolate gave 8 yellows and 
16 chocolates, but as I have no record of the preceding 
generation, I can not be sure that this result is compar- 
able to the last. It shows at least that a yellow female 
gave only two kinds of offspring. 

A **New Gray" Factor 
A word may be added about the *'new gray." In the 
original stock obtained from Mr. Horton there was a 



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458 THE AMERICAN NATURALIST [Vol. XLVHI 

gray female with a not-pure-white belly. She was not 
used in the main lines of the experiments described above. 
But she was kept in stock and bred with chocolates. 
About a year later I noticed in the offspring of a pair of 
cinnamon white-bellied mice a few mice that looked like 
chocolates, but which showed, on closer inspection, dis- 
tinctly ticked hair. One of these new grays bred to 
black (heterozygous) gave some chocolates, blacks, new 
grays, and one very dark, almost black, mouse with 
ticked hair.** The female was bred next time to a house 
mouse (gray gray-belly) and produced all gray gray- 
bellied oflfspring that had a dark coat, but not nearly so 
dark as that present when the new gray is heterozygous 
for black. Until further tests have been made it can not 
be stated whether or not the new factor belongs to the 
yellow-black system of quadruple allelomorphs. 

8 The resemblance of this mouse to the rabbit "agouti -black" homozygouB 
for black is very striking (Punnett, Jour, of Genetics, II, 1912). 



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THEBTEEN YEAES OF WHEAT SELECTION 

T. B. HUTCHESON 
Associate Agronomist, University of Minnesota 

Intboduction 

In 1901 the Minnesota Agricultural Experiment Sta- 
tion planted a number of varieties of wheat from the 
polonicv/m, spelta, turgidum, d/urum and wlgare types in 
foundation beds in order to have specimens of these diflfer- 
ent types always on hand for class work, hybridiza- 
tion or demonstration purposes. Six of these varieties — 
hedgrow {turgidum), Eussian {vulgare), common speltz 
(spelta), kamouka (durum), and Polish (1) and Polish 
(2) (varieties of polonicum) — have been grown continu- 
ously since that time and an effort has been made to 
improve them by selection. The method followed was 
that introduced at this station by Professor W. M. Hays 
and called the ''centgener^' method. 

The centgener method consists, briefly, in starting with 
individual plants, planting one hundred selected kernels 
from each plant at equal depths and at equal distances 
apart in separate plots. A plot of one hundred plants is 
called a centgener. Careful notes are taken on the plants 
in each centgener and at harvest time five or more of the 
highest yielding plants are selected from which the seeds 
for planting the next year are taken. From these five 
best plants from five to ten of the best heads are selected 
and thrashed together. One hundred of the largest and 
plumpest kernels are then selected out of the seed ob- 
tained by thrashing these selected heads, and these are 
planted in the centgener test the next year. This work is 
continued from year to year, each season the hundred 
best kernels from the five or more best plants being 
planted in succeeding centgeners. 

469 



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460 THE AMERICAN NATURALIST [VOL.XLVIII 

In 1908 an experiment was planned with the object of 
developing a strain of wheat which would have a minimum 
amount of culm exposed between the base of the spike and 
the upper leaf sheath, or in other words, to produce a 
short-necked variety of wheat. The ultimate purpose of 
reducing the neck lengths was to reduce the area of the 
stem exposed to the black stem rust. Since this rust 
ordinarily does little damage to that portion of the culm 
enclosed in the leaf sheath, it was thought that a short- 
necked wheat would be more likely to escape serious 
damage from stem rust than a long-necked kind. For 
this work individual plants were selected which had short 
necks and the seed from these were planted in separate 
centgeners. Each year at harvest time ten or more plants 
which appeared to the observer to have the shortest necks 
were selected from each centgener and measurements of 
their neck lengths were made and recorded. One hundred 
kernels were saved from these shortest necked plants 
each season for subsequent centgeners, thus making a 
continuous selection for short neck lengths. 

The data derived from the above experiments seems to 
throw some light upon the much-discussed question as to 
whether or not selection within a pure line can increase 
yield or change type enough to make it a desirable prac- 
tise from the practical breeder's standpoint. In both of 
the experiments, we have the requirements for a pure 
line satisfied. Wheat is a normally self -fertilized plant. 
Each centgener was started from a single head in 1901 
and these heads have bred true to type ever since. 

The long period of years over which this experiment 
has extended makes the data particularly valuable. One 
of the adverse criticisms to most pure line work is that 
it has not extended over a long enough period of time. 
Thirteen years are about as long as any practical breeder 
would be apt to keep up selection on one pure line and 
covers the longest period of continuous selection for a 
self-fertilized plant yet reported. 

Another criticism to pure line investigations is that in 



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No. 572] THIRTEEN YEARS OF WHEAT SELECTION 461 

many cases it has not appeared certain that the material 
studied was a pure line. Since the plants have bred true 
to type throughout the whole period of study, it is obvi- 
ous that this criticism will not hold for the data herein 
presented. 

The work haS been conducted at this station under the 
direction of Professor W. M. Hays from 1901 to 1905, 
under Professor E. C. Parker 1905 to 1908, under Pro- 
fessor Andrew Boss from 1908 to 1911 and under Pro- 
fessor C. P. Bull 1911 to 1913. 




Plate I. Average yield per plant for all varieties. X-X, fitted straight 

line. 

Selection to Increase Yield 
The varieties studied, the average annual yield of each 
variety and the average yield per plant for the six vari- 
eties under test are shown in Table I. In the years 1903 
and 1904 weather conditions were unfavorable, making 
it impracticable to obtain correct average yields per 
plant, so data for these years were omitted. However, 
selections of the best plants were made in these two 
seasons as in the others and the best seed from them 
were kept for planting, so the continuous selection for 
increased yield was uninterrupted. 



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462 



THE AMERICAN NATURALIST [Vol. XLYIH 



TABLE I 
Showing Yield Pee Plant — ^Yeaes 1901-1913 



Name of Variety 



Yield per Plant in Grs. 



1901 1902 1905 ' 1906 1907 1908 1909 1910 | 1911 1912 1918 



Hedgrow. . 
Russian. . . 

Speltz 

Kamouka. . 
Polish (1) . . 
Polish (2).. 



3.10 
1.00 
2.40 
1.60 
.80 
1.10 



2.80 
1.70 
1.80 



3.69 2.48 
3.67, 1.96 
3.99 2.99 



2.60 1.99 2.( 



1.30 
.95 



2.52| 2.04 
2.83' 1.97 



1.27 
1.71 
1.38 
1.39 
1.03 
1.26 



3.75 
2.74 
3.38 
3.31 
1.48 



2.49 2.65 2.02 .99,3.67 



1.95 1.37 2.70 

2.01 2.14 2.59 

1.67 1.36! 2.16 

1.91! 1.70 1.66 1.12 1.74 

1 1.61 1.31 1.78! .51 1.33 



2.71 2.17 
2.40 2.86 
2.19! 2.48 

1I 



Average 



1.65 



1.84 3.10! 2.35* 1.34 2.93| 2.22 2.18 1.83 1.24 2.36 



Selection to Incbease Height 
The average height of the plants for each year of the 
test is shown in Table II. Though no attempt was made 
to select for increased height, since a number of workers 
have shown that height in the small grains is distinctly 
correlated with yield, it is natural to suppose that the 
selected plants were among the tallest as well as "being the 
highest yielders of each year's crop. When this experi- 
ment was begun, it was not known that height and yield 

table n 

Showing Average Height Per Plant — 1901-1913 











Height in Inches 








Name of Virietj 


1901 


1902 


1905 


1906 


1908 


1909 


1910 


l$»ll 


1912 


1913 


Hedgrow 


36 
34 
34 
36 
40 
28 


41 
37 
38 
34 
38 
30 


42 
40 
37 
34 
41 
37 


43 
36 
47 
38 
38 
37 


46 
44 
44 
40 
42 


41 
41 
41 
40 
42 
35 


38 
33 
39 
32 
33 
31 


41 
36 
42 
38 
39 
38 


36 
35 
39 
36 
38 
31 


36 


Russian 


32 


Speltz 


35 


Kamouka 

Polish (1) 

Polish (2) 


33 
33 
32 


Average | 35 


36 


38 


39 


43 


40 


34 


39 


36 


33 



were correlated, so the figures on height were kept merely 
as a matter of general interest and with no idea that they 
would have bearing on the problem. Among those who 
later found height correlated with yield are Deneumostier 
(10),^ Love (ai),2 Myers (12),8 Leighty (^2)* and 



1 Deneumostier, C, 
1910. 



'Correlations in Wheat," Ann, Oemblouan, 20, No. 5, 



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No. 572] THIRTEEN YEARS OF WHEAT SELECTION 463 

Selection to Decbbasb Nbok-Lengths 
The result of the selection for short neck-lengths is 
shown in Table III. This is a clear illustration of how 
misleading short-term experiments may be. Had the 
experiment been discontinued at the end of the third year, 
the figures would have indicated that it was possible to 
modify this character very rapidly by selection. How- 
ever, in the following two years the neck-lengths seemed 
to revert to the mean of the pure lines, and the last year 
they were actually longer than when the experiment was 
started. The reduction in the first three years was prob- 
ably due to growing conditions. 



TABLE ni 
Showing Besult of Selection tob Shobt Necks 







Averago Neck L ngtb 


in Curre 






1909 


1910 


1911 


1912 


1918 


Series A 


7.4 
6.1 
6.8 
6.2 


1.86 
1.12 
1.66 
2.08 


.24 
.79 
.66 
.69 


7.34 
8.13 
7.63 

10.47 


9.64 


Series B 


11.6 


Series C 


8.21 


Series D 


13.82 



Discussion 
From the data presented in these tables, it is evident 
that there has been no permanent gain for these thirteen 
years of selection either in yield per plant, height of 
plant, or shortening of neck-lengths. The expected sea- 
sonal variations occur. A comparison of the yield of 
Haynes Blue Stem, which is grown extensively in Minne- 
sota, and was continued in the variety test without any 
attempt at selection throughout the whole period, with 
Hutcheson (13).«* 

2 Love, H. H., *'A Study of the Large and Small Grain Question," An, 
Bep, Am, Br, Asso., 7: 109-118, 1911. 

» Myers, C. H., * * Variation, Correlation and Inheritance of Characters of 
Wheat and Peas," Cornell University Thesis, 1912. 

4 Hutcheson, T. B., "Correlated Characters in Avena sativa, with Special 
Reference to Size of Seed Planted," Cornell University Thesis, 1913. 

«Leighty, C. E., "Studies in Variation and Correlation of Oats, Avena 
saiiva," Cornell University Thesis, 1912. 



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464 



THE AMEBIC AN NATURALIST [Vol. XLVIII 



the average yield of the selected varieties, is shown in 
Table IV. The average yield in bushels of the Haynes 
Blue Stem is also platted in comparison with the average 
yield of the selected varieties in Plate II. In 1912 a 
severe hail storm injured the variety plats so much that 




Plate II. Comparing seaj^onal fluctuations in selected lines with unse- 
lected Blue Stem. Solid line, yield per plant in grams for selected lines; 
dashed line, yield in bushels per acre for Blue Stem. 

it was thought best not to include the yield of the Haynes 
Blue Stem for that year. This gives an incorrect appear- 
ance to the curve, as it was extended just as if this year 
was present and midway between 3911 and 1913 in yield. 
It will be noticed from Table IV and Plate II that the 



TABLE IV 

Comparing Seasonal Fluctuations in Selected Lines with Unsblbcted 

Blue Stem 



1901 



1902 



1905 



1906 



1907 



Yield in grs. per 

plant for selected I 

lines I 1.65 1.84 3.10 2.35| 1.34 2.93 

Yield in bu. per 



1908 



acre for bluei 
stem 22.9 



1909 I 1910 1911 



2.22 



23.9 30.4 24.00 21.00 26.00 26.6 



1912 , 1918 



2.18 1.83 1.24 

I I 



2.36 



24.6 24.2 1 123.2 



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No. 572] THIRTEEN TEARS OF WHEAT SELECTION 465 

fluctuations from year to year agree very closely. These 
data indicate that increased yield is due to favorable 
environmental factors and not to improvement by 
selection. 

A comparison of the yield of each variety for the first 
five years of the test with that of the last five years is 
shown in Table V. The data in this table show that 
there is no significant difference in yield for these two 
periods; In Eussian and Polish (1) there is a slight 
increase in favor of the latter period, but in the other 
four varieties there is just as much decrease for this 
period. However, there is not enough difference in any 
case to indicate either permanent improvement or de- 
crease in yield. As far as these varieties are concerned, 
it seems that selection has brought about no permanent 
improvement. 

TABLE V 

GOMPAUNa THE YiELD OF THE FlEST-YEAB PERIOD WITH THAT OF THE LAST 

FivE-YEAB Period 





IstS-year Period 


Last 6-year Period 


Name of Variety 


Height 


Yield 


Height 


Yield 


Hedgrow 


41.6 
38.0 
40.0 
36.4 


2.67 
1.90 
2.61 
2.01 
1.64 
1.62 


38.4 
36.4 
39.2 
36.8 
37.4 
33.4 


2.34 


Kiimriftn 


2.18 


Spelta 


2.40 


Kamouka 


1.97 


Polish (1) 


39.8 
33.4 


1.61 


Polish (2) 


1.31 






Average ..1 38.2 


2.06 ! 36.5 


1.97 



A curve of the yields of the six varieties under con- 
sideration for the thirteen years of the test was plotted 
and a straight line was fitted to it, by the method of the 
least squares, to indicate the trend of the yield. This 
curve is shown in Plate I. There is a slight downward 
tendency in this straight line, but it is not enough to indi- 
cate a tendency toward decrease in yield. The line fitted 
to the curve of height (Plate III) also shows a slight 
tendency downward. 

The data herein cited are not sufficient for definite con- 



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466 



THE AMERICAN NATURALIST [Vol. XLVIII 



elusions. However, the indications are that from a prac- 
tical breeder's standpoint permanent improvement in 
pure lines in small grains, if possible, is certainly not 
rapid or apt to be very marked. Thirteen years of selec- 





















4 


^ 
























/ 


V 








^ 


u 






/ 

J 


A 
V 








^ 








/ 


\ 








9« 


19 




/ 






\ 






J 


_J^ 




/ 






\ 7 


^ 




ns 


U 


^^ 


7 — — 






J /l >v M 




a 




,/ 








v^ 


"" \~"--; 


f 


1: 


15 ^ 


7^ 








17 


V 




* 












JL 






« 


t2 












3 
























% 


I 


\ I 


1ZE2 


"5 "3 


«i r 






1 


1 




P 




~* "•! 


"f "IB 





Plate III. Average height of all varieties. X-X, fitted straight line. 

tion covers considerable time and expense, and, as far as 
can be seen from the varieties reported in this paper, it 
has resulted in no permanent improvement. This would 
suggest that some other line of improvement must be 
sought. It is probable that much more rapid progress 
could be made by segregating pure lines from mixed 
populations and combining the desirable characters of 
these lines by hybridization. 



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PATTERN DEVELOPMENT IN MAMMALS 
AND BIRDS 

n 

GLOVER M. ALLEN 
Boston Society op Natural History 

Partial Albinism in Wild Mammals 

Partially albinistic individuals of species that normally 
are wholly pigmented, occur frequently in a wild state, 
and almost any large series of a given species may con- 
tain a few. I have examined many such, in which it was 
perfectly evident that the white mark was due to areal 
restriction of some one or more of the primary pigment 
areas just as described in the various domestic species. 
It is apparent that the white markings in both are quite 
comparable, but in species under domestication no agency 
seems present whereby such pied individuals are elimi- 
nated, whereas in a wild state the sudden acquisition of a 
large amount of white in an individual would not only 
render him too different from his fellows, but might put 
him at a disadvantage because of a conspicuousness to 
which as a species he had not yet become accustomed. 

There are many other species in which, as we now see 
them, white markings form a permanent and normal part 
of the pattern. Among those in which these white mark- 
ings are few or simple, it is often evident that they are 
merely prjjpary breaks between the pigment patches that 
have become more or less fixed by long periods of selec- 
tion, whether natural, sexual or otherwise. As I shall 
endeavor, tg^^how, there are species in which a beginning 
has alreaa^ been made towards the development of a 
pied pattern, though it has not yet become well fixed* 
Still other species show a more complicated white and 
pigmented pattern, the white portions of which can not 
readily be derived from primary breaks alone. Such I 
take to be highly developed patterns and make no attempt 

467 



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468 THE AMEBIC AN NATURALIST [Vol. XLVIII 

to analyze them here. Examples of this type are seen in 
the zebra, the spotted skunks {8pilogale)j the striped 
weasel {Ictonyx), Probably more than one factor is 
responsible for some of the combinations of stripes and 
spots seen, for example, in certain spermophiles (Citellus 
13-Uneatus) J but I shall not now attempt a discussion of 
these. 

One of the most frequent manifestations of pigment 
reduction in mammals is the presence of a white spot in 
the normally pigmented forehead. This is due primarily 
to the reduction of the ear patches, which fail to meet at 
their median edges. Perhaps, too, the apparent loss of 
the crown patch in some mammals still further tends to 
lessen the amount of pigment production at this point. 
Babbits and hares very often have more or less white in 
the forehead, but none of the species has developed this 
sufficiently to make it a permanent mark. Moseley in his 
^'Naturalist on the Challenger,'^ speaks of a ''black 
variety'' of wild rabbit — doubtless introduced — "with a 
white spot on the forehead" as occasionally found on 
Teneriffe, Canary Islands, but this mark is common, 
and I have seen it in such widely sundered species as the 
eastern varying hare of New Hampshire and the black- 
necked hare native to Java. A specimen of Leisler's bat 
{Nyctalus leisleri) in the Museum of Comparative Zool- 
ogy has a white spot in the middle of the forehead and 
another on the mid- ventral line of the abdomen — ^the first 
a primary break between the ear centers, the second 
probably a ventral primary break between tjig^e of the 
sides. Among the Insectivora, the West ]pdiah Solen- 
odon paradoxus has a white patch at th6 nape of the 
neck which has become a permanent part of *^s pattern. 
It is clearly the enlargement of a primary D'reak sepa- 
rating the ear patches and neck patches on the median 
dorsal line. It is a fact of much interest that in a con- 
siderable series of this species in the collection of the 
Museum of Comparative Zoology hardly two have it 
developed alike, but it varies from a few white hairs to 



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■?^.i 



y 



No. 572] PATTERN DEVELOPMENT 469 

a large patch 15 X 10 nun. wide. Evidently it has not 
yet become precisely defined in its limits, though now a 
permanent mark of the species. 

White marks in the forehead are common among the 

species of the Mustelidae or weasel family. A narrow 

^hite median line is present in the Javan mydans and in 

*he skunks {Mephitis) as part of the permanent pattern. 

In the badger (Taxidea) a white line is not only pres- 

^^t on the forehead, but it is often extended medially so 

1^® to separate the pigment patches of both sides of the 

^ ^y. In the New York weasel (Mustela noveboracensis) 

^^ the eastern United States a few white hairs are often 

/>7tesent on the forehead, and other instances could be 

xnixlti plied. Among monkeys, a white spot on the nose is 

pr&s ^nt in some species of Lasiopyga, and in an allied 

^en.xi.s Rhinostigma, it is elongated vertically to form a 

wrZiit^ streak. 

-A^ 3ret more illuminating case is that of the Muskeget 

^e^c^Ila mouse {Microtus breweri) a derivative of the 

^^^t^^oM^ignmOiOn brown meadow mouse of the New England 

^a^^ctHand. On this island of white sand oflf the Massa- 

jix^^ ^^tts coast, a pale variety has developed which is very 

.^^^izMzuct from that of the neighboring shores. Not only 

^i* .^a paler race, but albinism also has begun to appear, 

^ "fcii^^ ,«it occasional individuals have a white fleck between 

te ^^ ,^rs, showing the drawing apart of the ear patches. 

Of ^^i^ series of 62 specimens in the collections of the 

M^-^^-^^^xma of Comparative Zoology and the Boston Society 

0^ -^^"^ .^^tural History, no less than 13 had such white flecks, 

^^^^ ^Z3ne had in addition a white spot just in advance of 

i^^ ^shoulders, marking the line of separation between 

^^c^'lsi and shoulder patches. In our studies on the hered- 

\^^^ ^i>f coat colors in mice, Professor Castle and I dis- 

c^^r^ored (Allen, 1904; see also Little, 1914) that the pied 

wyxi^ition is recessive in the Mendelian sense towards 

^OcLfe self colored, so that partial albinos bred to wholly 

^Ygicaented mice produce in the second generation, if 

mterbred, 25 per cent, of spotted young. The figures 



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470 THE AMEBIC AN NATURALIST [Vol. XLVIH 

given above (13 in 62) are near this in case of the Muske- 
get mouse, but the matings are of course more promiscu- 
ous. The case is interesting in connection with the 
studies of Ramaley (1912) and Pearl (1914), tending to 
show that in a mixed population the recessives may in- 
crease so as to exceed the dominants. Although the 
spotted mice do not, in case of this species, exceed the 
unspotted individuals, they nevertheless are of far more 
frequent occurrence than they are in the mainland repre- 
sentatives of the species. This accords with the fact that 
island-living mammals are very conunonly albinistic, and 
the cause is doubtless that the population is much more 
inbred, so that the recessive condition of partial albinism 
is more likely to be propagated than if successive genera- 
tions have a wider range over which to spread. It seems 
probable that heredity will tend to increase the propor- 
tion of spotted mice of Muskeget, and that if this condi- 
tion is disadvantageous, a large part of the spotted indi- 
viduals will be killed off, yet in the course of time they 
may become adjusted to this condition and will survive 
in increasing proportion till the white mark becomes 
characteristic of all the animals. Cory (1912) records 
the capture of seven muskrats at Hayfleld, Iowa, all of 
which were uniformly marked, having a white ring around 
the neck and the entire underparts, feet, and end of tail 
white. I can think of three causes influencing the status 
of such white markings. These markings may be in- 
herited in a purely automatic way as unit characters; 
but if thus inherited they may be (1) increased through 
selection, natural or sexual; or (2) eliminated by the same 
agent; or (3) they may be, at first, of no influence at all 
in the economy of the animal and persist or not, accord- 
ing as they are heritable. 

I have mentioned that island mammals tend to be more 
albinistic than their mainland representatives. Other 
cases may be mentioned, as the common squirrel (Sciurus 
vulgaris leucurus) of Great Britain, which differs nota- 
bly from that of the continent in having frequently a 



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No. 572] PATTEBN DEVELOPMENT 471 

white or whitish tip to the tail, often for one half its 
length. A similar white tip is occasionally seen in our red 
squirrel {8. hudsonius) as an albinistic mark, and is due, 
of course, to the terminal restriction of the rump patches. 
The deer of Whitby Island, Puget Sound, are said to be 
much marked with white, and sundry marsupials of 
Papua as well as the monotreme Zaglossus are subject to 
white markings. In the cuscus {Pseudochirus) the pig- 
ment is sometimes restricted to small patches and round 
spots scattered on the back, those in the region of the 
shoulder of a different color from those of the side and 
rump patches. Another instance is that of the white- 
footed mouse of Monomoy Island, Massachusetts, the 
mid- ventral parts of which are pure white to the roots of 
the hairs, an albinistic condition to be clearly distin- 
guished from that in which the belly appears white, but 
only because of the white tips to the hairs whose bases 
are dark-pigmented. 

The restriction of the rump patches so as to produce 
a white tail-tip is common among mammals. It is found 
in occasional specimens of many species as the shrew mole 
{Blarina)y Brewer's mole (Parascalops), the meadow 
jumping mouse {Zapus)^ the white-footed mouse {Pero- 
myscus)y and squirrels (Sciurus). In some it has be- 
come developed as a permanent and characteristic mark, 
as in the woodland jumping mouse {Napceozapus)j the 
red fox {Vulpes)^ such genera as Hydromys, Tylomys, 
the Virginia opossum (Didelphys virginiana), the tree 
kangaroos {Dendrolagus). In many others a pure white 
beUy is developed through ventral restriction of the 
shoulder and side patches. 

Among ungulates the break between the ear patches 
has been developed to form a broad white blaze from 
forehead to nose in case of the blesbok (Damaliscus 
albifrons) of South Africa and in related species in 
East Africa. The chevron-mark on the forehead of cer- 
tain antelopes is possibly a specialized development of 
the same thing. 



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472 TRE AMERICAN NATURALIST [Vol. XLVIU 

White buttock patches are present in several unrelated 
ungulates — as the pronghorn {Antilocapra), the wapiti 
{Cervus canadensis) ^ and the Rocky Mountain sheep 
(Ovi'S canadensis). Probably these are the result of 
restriction or total inactivity of the pigment patches 
covering the rump. 



Fio. 42a. Diagram Showing the Pigmented Patches op a Partiallt ALBi!fO 

Dbbb. 

Among the deer family white is generally confined to 
the under surfaces and the primary white breaks have not 
been developed to form patterns. Albinistic deer are 
fairly common, however, and in Fig. 42a I have made a 
tracing from a photograph showing the side of a par- 
tially albino doe in which areal restriction of pigment has 
taken place in such wise that the primary patches are 
all indicated, and separated from those of the opposite 
half of the body by a median dorsal white line. The ear 
and the neck patches are joined, but a few small islands 
of pigment are left here and there, much as in cows. 

In the young of many deer and in the adult of such 
species as the axis deer, a spotted pattern is developed. 



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No. 572] PATTERN DEVELOPMENT 473 

There is an obvious tendency for the spots to become 
arranged in longitudinal rows, and intermediate stages 
may be found in which they coalesce to form broken lines. 
There is little doubt that the complete white stripes 
occurring in part of this pattern were formed originally 
through the coalescence of rows of white spots. In the 
tapir a somewhat similar spotted pattern is found in 
the young, while the adult Malayan tapir has lost the 
shoulder and side patches, producing thus a white-bodied 
animal, pigmented to the back of the foreleg and on the 
buttocks and hind legs. Among the ground squirrels 
(Citellus) a beautiful series can be picked out showing 
the transition from a uniform grizzled mixture of ticked 
hairs to indistinct spotting, then rows of white spots, and 
finally broken and complete longitudinal stripes. The 
production of these stripes I believe to be due, not to the 
development of breaks between the primary pigment 
patches, but to the action of a factor which is the negative 
of the so-called ''English'' marking in rabbits, so that 
instead of the development of scattered small pigments 
spots there are formed, instead, spots without pigment. 
That it is possible to evolve a striped pattern from spots 
through selection, I have no doubt, and indeed, it is gen- 
erally believed. On the other hand, it is quite possible 
that the converse may happen, and spots result through 
the breaking up of stripes. According to the experiments 
of Professor Castle and Dr. MacCurdy, however, it seems 
to be a diflScult matter to fix a given marking by rigid 
selection, yet it must be admitted that a few years' work 
even of careful breeding is nothing in comparison with 
the age-long selection that may have been at work on the 
species. That it is a difficult matter to produce a given 
pattern is further evidenced by the fact that in many 
species in which white markings regularly occur as part 
of the pattern, these are subject to great individual 
variation in their extent, showing that they are even yet 
not wholly definite. 
It was formerly urged against evolutionary doctrine 



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No. 572] 



PATTERN DEVELOPMENT 



under side of the specimens. In the large coastal race of 
mink found from southern Maine to the Carolinas {M, v. 
lutreocephalus), the entire pelage is usually brown, ex- 
cept for the chin which is white. Occasional white marks 
are present in some specimens along the mid-ventral 
line of the throat and chest, and between the hind legs. 
In the smaller typical M. vison of northern New England 
northward the white marking is apt to be more extensive, 
and in no two individuals exactly alike. The diagrams 
show the ventral markings of a few specimens from New 
England and Nova Scotia. In Fig. 43 the amount of 
white is very small. The chin spot, which represents the 
beginning of a break between the two ear patches at their 
antero-ventral extremity, is always present and has be- 
come now a fixed mark of the species, though variable in 
extent. A slight break in the center of the chest shows 
where the two shoulder patches have failed to meet, and 
a white spot at the anal region indicates a like restriction 
of the rump patches. Similar spots appear mid-ventrally 
in Fig. 44, with the addition of a few white hairs, medially 
at the upper throat, where the ear and neck patches join, 
and a few more on the lower throat at the line of union 
of the neck patches of opposite sides. In Figs. 45 and 46 
no break is present on the abdomen, but in the former 
figure, a large transverse break has appeared on the 
upper throat where the ear patches fail to unite with the 
neck patches and with each other, and a median line runs 
forward to join the white of the chin, showing the greater 
restriction of the ear patches ventrally. An imperfect 
separation of these patches along the center of the throat 
has taken place in Fig. 47, and a more considerable break 
occurs in the same place in Fig. 46. In the Pacific Coast 
mink {Mustela vison energumenos) a well-developed 
white patch on the chest is rather characteristic, some- 
what larger than in Fig. 45. This is due to the ventral 
restriction of the shoulder patches which fail to meet 
below. In Fig. 46 this white area is seen with a tongue 
extending upon the center of the lower throat, and on to 



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476 THE AMEBIC AN NATURALIST [Vol. XLVm 

one fore leg, as well as in the mid line of the thorax, mark- 
ing nearly the anteroposterior limits of the shoulder 
patch. The neck patches are not separated in this figure 
but have become so in Fig. 48, so that a continuous line 
of white runs from chin to chest. In Fig. 47 the shoulder 
and the side patches have both failed to join venfrally, 
and thus a broad white line is formed down the center of 
the belly from the conjoined neck patches to the rump 
patches. If all these breaks were to be present in a single 
animal, there would be a narrowed white area along the 
entire ventral side of the body from chin to anus, extend- 
ing on to the lower side of the fore legs. Practically 
this condition exists in another species of the same 
genus, Streator's weasel (Mustela streatori) of the 
Pacific Coast, in which the throat, chest and belly are 
white but the width and boundaries of the white area are 
very variable in different individuals. It is therefore in 
a stage beyond that which the minks have reached, yet it 
has not attained the stage in which the white area is of 
definite and rather constant bounds, as in certain other 
weasels, for example Mustela noveboracensis, in which 
the white, of the belly extends nearly or quite to the 
lateral border of the body, but in different individuals 
varies slightly, and M. cicognanii, in which the white area 
of the belly constantly extends to the lateral boundary of 
the venter from throat to anus. This is the condition 
toward which the mink is tending. 

Another interesting case in which a pattern mark ap- 
pears to be evolving through the fixation of a primary 
break between pigment patches is that of the so-called 
tayra of South America (Tayra barbara) a large Muste- 
lid. The Central American race (biologice) of this animal 
is wholly black, but the typical subspecies of Brazil and 
northern South America is subject to a varying amount 
of reduction in pigmentation. Curiously, this takes place 
at the posterior end of the neck patches or at the anterior 
part of the shoulder patches. Three of five specimens in 
the Museum of Comparative Zoology are marked in this 



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No. 572] 



PATTERN DEVELOPMENT 



477 



way. All have a triangular patch of white at the base of 
the throat ventrally, as a break between neck and shoulder 
patches and a partial separation of the neck patches 
from each other. Each has a dorsal mark of white ; in the 
first a narrow linear break between the shoulders ; in the 
second a broader transverse mark, and in the third a 
square patch of white occupying nearly the width of body 
between the shoulders to the base of the neck. The white 
throat marking increases in e^^tent from first to third, 
just as does the dorsal marking. Probably in time this 
white mark, now of irregular size and appearance indi- 
vidually, will become a permanent part of the pattern. In 
this animal the entire head and neck are a grizzled gray 
as far back as the posterior limit of the neck patches, and 
the rest of the body is black. This, then, shows that the 
pigment patches of head and neck are differentiated in 
color as well, from the patches of the rest of the body. 
The occurrence of white markings in the back is relatively 
uncommon in mammals, though white on the und