SEX IN ANIMALS 549 
tration may be illustrated by a few typical cases. In sheep there are 
breeds which are hornless in both sexes, hornless in the female and 
horned in the male, and horned in both sexes. When both sexes are 
horned there are usually rather striking differences in the horns, 
those of the male being the better developed. Fig. 215 shows this for 
Dorset sheep which have been used in such experiments. The effect of 
castration in such breeds has been studied by Marshall. He finds that 
as a result of castration of males in those breeds in which males only are 
horned, the horns fail to develop. In breeds in which both sexes are 
horned castrated males develop horns like the females. 
The above effects are of interest when taken in connection with studies 
of inheritance of horns in sheep. Thus Wood has studied crosses between 
Fic. 215.—Dorset sheep showing the differences in development of horns in the two sexes, 
(After Shaw and Heller.) 
Dorset and Suffolk sheep. The latter are hornless in both sexes. The 
F, of this cross consists of horned rams and hornless ewes. The F»2 con- 
sists of horn and hornless individuals in both sexes in the approximate 
ratio: 
3 horned o& :1 hornless & :1 horned 2 :3 hornless ¢. 
Bateson and Punnet assume that the horned breeds are of the constitu- 
tion HH XX, female, and HHXY, male; and the hornless, hhX_X, female, 
and hhX Y, male. The F; then consists of HhXX, hornless females, and 
HhXY, horned males. Here they make the assumption that one dose 
of the factor H results in the production of horns in the male on account 
of the sex relations, but in the female two doses are necessary for the 
development of horns. This hypothesis does not account for those 
breeds which are horned in the male and hornless in the female, but it 
is not absolutely necessary that it should. We see here, however, a 
basis for the modifications of horns following castration for evidently 
the factor complex for the horned condition reacts differently in male and 
female. 
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