IX SEX 85 



from the 3 : i ratio obtained in F^, as well as from 

 the fact 'that the Fj birds mated with golds give 

 equal numbers of golds and silvers. 



(2) Femaleness is dominant to malencss, the female 

 being heterozygous for a factor, F^, which is not 

 present in the male. This assumption is in accord- 

 ance with the fact that the sexes are produced in 

 equal numbers. The female must be supposed to 

 produce equal numbers of female-producing eggs 



containing F, and of male- 



, . 1 • 1. J Silver Gold 



producmg eggs which do j' x • 



not contain the factor. I 



Since the male does not [ 1 



carry F, this factor cannot ® * 



occur in any spermato- 

 zoon. Every female, on ^ [ 

 this view, receives the 

 factor for femaleness from 



F, 



1 1 



c? (^ 9 ?- 



Fig. 18. 



Virx- rrtr\t-hnr Scheme illustrating the cross between a 



ner motner. ^i,^^^ ^^^^ ^^^ ^ g^i^ ^g„_ b,^^^. 



(3) The silver hen is ^,^S^'^it')j^t^S^ 

 always heterozygous for JTilL^ygtUnvers. '"'''''' '^""'^ 

 the silver factor, S, as 



well as for that for femaleness, F. Moreover, it 

 must be supposed that when she forms eggs some 

 form of repulsion occurs between the two factors, of 

 such a kind that they will not enter into the same 

 gamete. The eggs of such a bird must be supposed 

 to be of two kinds and of two kinds only, viz. Fs 

 and /S. 



If wc make these assumptions, the experimental 

 facts are open to a simple explanation, as shown 

 graphically on Plate V. The original silver male 

 was homozygous for 5. As he cannot contain F 



