SEX 



101 



the Fj male birds produced by this cross is ffPpli 

 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 

 these factors. The 



nature of the F 2 genera- 1 91 Ff PP I{ ffppii 



tion in each case is gives &ives 



gametes gametes 



in harmony with the p . .. , . . 



above scheme. As, f p j j x 

 however, it serves to 



illustrate certain points i 



i i 



in connection with in- FfPpii ffPpli 



termediate forms we [?] [(?] 



shall postpone further 



Scheme to illustrate the nature of the F t 



Consideration Of it till generation from the Brown Leghorn hen 



and Silky cock (cf. Fig. 22). 



we discuss these 



matters, and for the present shall limit ourselves to 

 the explanation of the different behaviour of the F x 

 males and females when crossed with the Brown 

 Leghorn. And, first, the cross of Brown Leghorn 

 female by F l male. The Brown Leghorn hen is on 

 our hypothesis Ffppli, and produces gametes Fpi and 

 fpL The F! cock is on our hypothesis ffPpli, and 

 produces in equal numbers the four kinds of gametes 

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

 these two series of gametes is given in Fig. 24. 

 Of the eight different kinds of zygote formed only 

 one contains P in the absence of /, and this is a 

 female. The result, as we have already seen, is in 

 accordance with the experimental facts. 



