108 ORIGIN OF SOMATIC 



offers no explanation of this, but it obviously 

 suggests that some trace of the original dimorphism 

 of the sheep in this character was retained in both 

 horned and hornless breeds. We may suppose that 

 the factor for horns had disappeared entirely from 

 the hornless sheep by a mutation, but in the horned 

 breed another mutation had been a weakening of the 

 influence of the sexual hormones on the development 

 of the character, which, as in all such cases, is really 

 inherited in both sexes. In the i^j, when the horned 

 character in the female is only inherited from one 

 side, the hereditary tendency is not enough to 

 overcome the influence of the absence of the testis 

 hormone and presence of the ovarian hormone, and 

 so the horns do not develop. The Mendelian merely 

 sees a relation of the character to sex, but overlooks 

 entirely the question of the dimorphism in the 

 original species from which the domesticated breeds 

 are descended. Similarly, with regard to cattle 

 where it has been found that hornlessness is domi- 

 nant or nearly so in both sexes, no reference is 

 made to the opposite fact that wild cattle have 

 horns in both sexes and are not dimorphic in this 

 character. 



Bateson proceeds to consider colour-blindness as 

 though its heredity were of similar kind. He refers 

 to it as a male character latent in the female, and 

 remarks that we should expect that disease or re- 

 moval of the ovaries might lead to the occasional 

 appearance of colour-blindness in females. He also 

 discusses the case of Abraxas grossulariata and its 

 variety lacticolor, and other cases of sex-linked 

 heredity, apparently with the idea that all such 

 cases are similar to those of sexual dimorphism. A. 

 lacticolor occurs in nature only in the female sex, and 



