IX 



SEX 



93 



inhibitor factor (/), and in constitution therefore is 

 Ffppli. Owing to the repulsion between F and / 

 the gametes produced by such a bird are Fpi and fpl 

 in equal numbers. All the gametes produced by 

 the Silky cock are fPi. Hence the constitution of 

 the Fj male birds produced by this cross is ffPpIi 

 as before, but the female birds must be all of the 

 constitution FfPpii. The Silky cock transmits the 

 fully pigmented condition to his daughters, because 

 the gametes of the Brown Leghorn hen which con- 

 tain the factor for femaleness do not contain the 

 inhibitory factor owing 



to the repulsion between [?] F^PP'i ffPPii L^J 



these factors. The 

 nature of the F^ genera- 

 tion in each case is 

 in harmony with the 

 above scheme. As, 

 however, it serves to 

 illustrate certain points 

 in connection with in- 

 termediate forms we 

 shall postpone further 

 consideration of it till we discuss these matters, 

 and for the present shall limit ourselves to the 

 explanation of the different behaviour of the Fj 

 males and females when crossed with the Brown 

 Leghorn. And, first, the cross of Brown Leghorn 

 female by Fj male. The Brown Leghorn hen is on 

 our hypothesis Ffppli, and produces gametes Fpi and 

 fpl. The Fj cock is on our hypothesis ffPpU, and 

 produces in equal numbers the four kinds of gametes 

 fPl, fPi, fpl, fpi. The result of the meeting of 



Fig. 23. 



Scheme to illustrate the nature of the Fj 

 generation from the Brown Leghorn hen 

 and Silky cock (cf. Fig. 20). 



