IX SEX 91 



slight amount of pigment and birds without pigment. 

 And this was true for both the deeply pigmented 

 and the slightly pigmented types of F^ hen. But 

 when the F^ cock was mated to a Brown Leghorn 

 hen, a definite proportion of the chicks, one in eight, 

 were deeply pigmented, and tJiese deeply pigmented 

 birds were always females (cf. Fig. 2 1 ). And in 

 this respect all the F^ males behaved alike, whether 

 they were from the Silky hen or from the Silky 

 cock. We have, therefore, the paradox that the F^ 



(Brown Leghorn) Silky 



( ' —1 



(Brown Legh.)c? X ? (^ X 9 CBrown Leghorn) 



Fig. 21. 



Scheme to illustrate the result of crossing Fj birds (^e.g. Brown Leghorn x Silky) 



with the pure Brown Leghorn. 



hen, though herself deeply pigmented, cannot trans- 

 mit this condition to any of her offspring when she 

 is mated to the unpigmented Brown Leghorn, but 

 that, when similarly mated, the F^ cock can transmit 

 this pigmented condition to a quarter of his female 

 offspring, though he himself is almost devoid of 

 pigment. 



Now all these apparently complicated results, as 

 well as many others to which we have not alluded, 

 can be expressed by the following simple scheme. 

 There are three factors affecting pigment, viz. (i) 

 a pigmentation factor (/^) ; (2) a factor which 

 inhibits the production of pigment (/) ; and (3) a 



