258 BREEDING 



their normal size in the male hybrids from the 

 same cross. And this inhibiting something is, as I 

 have said, identified with the dominant factor which 

 is present in the zygotic constitution of the female 

 and absent from that of the male. Those of my 

 readers who are familiar with Otto Weininger's 

 theory, expounded in his " Sex and Character," of 

 the difference between the two sexes will detect a 

 very close parallel between it and the Mendelian 

 view. 



Evidence derived from widely different and abso- 

 lutely independent lines of inquiry tends to support 

 the Mendelian theory. But there is a qualification. 

 The various lines of evidence point to the con- 

 clusion that one sex is hybrid and the other pure ; 

 but they do not all point to the same sex as being 

 hybrid and pure respectively. 



Let us examine them separately. We will deal 

 first with the only one, of those I propose to consider, 

 which, like the Mendelian theory, points to the 

 female as the hybrid. This is contained in a book 

 entitled " The Causation of Sex," by Dr. E. Dawson, 

 which appeared recently. The theory, however, was 

 first enunciated at the Obstetrical Society in 1900, 

 so that there is no possibility of the author having 

 heard of the Mendelian theory of sex, even if the fact 

 that he does not refer to it were not suflB.cient evidence 

 of this. Dr. Dawson thinks that the male plays no 

 part in determining sex in the human species, that his 

 germ- cells are all indifferent in respect of sex ; the 

 female, on the other hand, gives rise to two kinds of 



