REPRODUCTION AND SEX 331 



(d) FOURTH THEORY. — Thai maleness and femaleness are Men- 

 delian characters. 



A Mendelian interpretation of sex, first suggested by Strasburger, 

 has been developed by Castle, Correns, Bateson, and others. As 

 Wilson points out, the interpretation has taken "three forms, which 

 exhaust the a priori possibihties. These are, first, that both sexes 

 are sex-hybrids, or heterozygotes (Castle); second, that the male 

 alone is a heterozygote, the female being a homozygote recessive 

 (Correns) ; third, that the female is the heterozygote, the male being 

 a homozygote recessive" (Bateson). 



Let us state the third form of the Mendelian interpretation, which 

 is supported by a number of striking facts, especially in regard to 

 the common currant-moth (Abraxas grossulariata) and the canary. 



Assuming that there are sex-determinants, "factors" or "genes" 

 of maleness and femaleness, the experimenters suggest: (i) that 

 these behave as Mendelian units, femaleness being always dominant 

 over maleness; (2) that female individuals are heterozygous as 

 regards sex (having maleness recessive) and that they give rise to 

 equal contingents of male-producing and female-producing ova; 

 (3) that male individuals are homozygous as regards sex, being 

 without the femaleness factor, and give rise only to male-producing 

 spermatozoa; (4) that when a male-producing spermatozoon 

 fertilises a male-producing ovum the result is, of course, a male, 

 and that when a male-producing spermatozoon fertilises a female- 

 producing ovum the result is a female, femaleness being by hypoth- 

 esis dominant over maleness. 



Doncaster refers to the confirmation which the Mendelian theory 

 of sex receives from the results of castration. In Vertebrates the 

 castration of the young male may prevent the expression of mascu- 

 line features, but it does not induce the expression of feminine 

 characters. This may mean that the male is homozygous, that is to 

 say, purely masculine without any feminine characters latent. We 

 would, however, point out that in many cases there is a lack of 

 positiveness in the feminine characters ; while the masculine char- 

 acters are positive and distinctive. In other words, there might be a 

 good deal of latent femininity in the castrated male, without there 

 being much to show for it. It would be extremely interesting to 

 experiment with some case like the Red-necked Phalarope, where 

 the female bird is the more masculine of the two. 



The fact that the proportions of the sexes are sometimes very 

 variable, as Heape points out in regard to canaries, does not of 

 itself tell against the view that the ova are determined at an early 

 stage to be male-producers or female-producers. There may be a 

 process of discriminate selection during the maturing of the ova, 

 and we know that in higher Vertebrates the possible ova do not all 

 come to maturity. 



