May 17, 1912] 
yellow female is YY. The constitution of 
these four parent forms would then be: BB, 
black female; B—, black male; YY, yellow 
female; and Y —, yellow male. 
If then we make the cross yellow male, 
Y—, X yellow female, YY, all the young 
should be yellow, one half being males and 
one half females. In this cross 5 young have 
been obtained, 3 males and 2 females, all 
yellow. 
If we make the cross black female, BB, 
X yellow male, Y —, we have in F, two types 
of individuals, viz., BY, tortoise females, and 
B—, black male. Theoretically these two 
types should be formed in equal numbers; 
actually the tortoise females are 8, the black 
males 7. The reciprocal cross is yellow fe- 
male, YY, X black male, B—; F, has two 
types of individuals, viz., BY, tortoise female, 
and Y —, yellow male. This expectation co- 
incides with the facts observed by Doncaster. 
We have, however, an important cross under 
way which must be carried out more fully 
before the hypothesis, given above, can be con- 
sidered as proved. This mating is: tortoise 
female, BY, X yellow male, Y—. The ex- 
pected result is BY, tortoise females; YY, 
yellow females; B—, black males; and Y —, 
yellow males. One litter has been obtained 
from this cross; it contained one tortoise fe- 
male, one black male and three yellows (dead), 
the sex of which was unfortunately undeter- 
mined before the earetaker discarded them. 
It is interesting to note that Doncaster cites 
this mating as producing “blacks, tortoises 
and oranges,” though he does not record the 
Sexes. 
The cross tortoise female black male has 
been recorded by Doneaster. It gave tortoise 
females, orange males, black females and black 
males. By the hypothesis here suggested this 
is to be expected. Thus tortoise female, BY, 
black male, B—, should give BB, black 
females; B—, black males; Y—, yellow 
males; and BY, tortoise females. 
Male “tortoise shells” occasionally occur, 
and it seems probable from their rarity that 
they are due to some distinct mutation such 
as that which produces tortoise guinea-pigs, 
SCIENCE 
785 
and not to heterozygosis between black and 
yellow. Theoretically, if such were the case, 
tortoise females of a similar nature might be 
produced. Such animals would be indistin- 
guishable externally from the common form 
of “tortoise,” but would differ in gametic 
composition, and therefore in their behavior 
in crosses. 
So far as first-hand evidence goes the ob- 
served experimental facts are best explained 
by the hypothesis outlined above, which con- 
siders the factor for black coat color in cats 
to be linked with the X element, and there- 
fore to be sex limited. Doncaster’s suggestion 
that tortoise is merely the female heterozygote 
obtained in crosses between yellow and black 
would not explain the fact that reciprocal 
erosses of black with yellow produce males 
differing in color, one cross producing black 
males, the reciprocal cross producing yellow 
males. Indeed the last-mentioned fact in 
itself makes the case unique among mammals. 
Tf, then, the hypothesis of “ sex-limited ” char- 
acters outlined above is found to be substan- 
tiated by the cross, tortoise female * yellow 
male, we shall have established a case of the 
same general character as those described by 
Morgan as occurring in Drosophila. Further 
experiments bearing upon the matter are in 
progress. 
C. C. Littie 
April 23, 1912 
THE AMERICAN PHILOSOPHICAL SOCIETY 
THE annual general meeting of the American 
Philosophical Society was held in the rooms of 
the society at Philadelphia, April 18 to 21 inelu- 
sive, and constituted perhaps the most notable 
series of sessions ever held by the society. The 
papers were all of a high order of merit and pre- 
sented in many cases for the first time the results 
of original investigation by the authors. 
The meeting was opened on Thursday afternoon, 
President W. W. Keen, LL.D., in the chair, when 
the following papers were read: 
Some Former Members of the American Philo- 
sophical Society: THOMAS WILLING BALcH. 
The writer said that besides Franklin, the 
founder of the society, Washington, Jefferson and 
Cleveland were members. Many other political 
