W. Bateson and R. C. Punnktt 197 



hypothesis these birds are in constitution FfPpii and consequently 

 should give the same result as the deeply pigmented ^i % when crossed 

 with a pure Silky ff. We have made this cross on two occasions and 

 in accordance with expectation all the chicks were deeply pigmented 

 (cf. Table IX). 



TABLE IX. 



5. Crosses with deeply pigmented F^ birds. 



In the course of our experiments we have made crosses with two 

 deeply pigmented F^ birds, viz. f^ 40 (from Pen 15, 283 of 1907) and 

 % 150 (from Pen 23, 114 of 1907). Each of these birds was as deeply 

 pigmented in the adult stage as the pure Silky, and when bred together 

 they gave only fully pigmented offspring (12 ^f^ and 1\ % %). <^ 40 

 was also mated with a pure Brown Leghorn $ and gave 2\ ^^^ with 

 some pigment together with 33 deeply pigmented % $. But he is 

 recorded as giving also one deeply pigmented ^ and 2 $ $ which 

 were not deeply pigmented. To these exceptions we shall return 

 and will merely state here that we regard them as due to a peculiarity 

 in the behaviour of the Brown Leghorn hen. $ 150 behaved like a 

 pure Silky when crossed with a Br. L. {/• (p. 192), and we look upon 

 both these F^ birds as of the constitution PPii. 



6. The ppii strain. 



In this account we have so far been concerned with the results of 

 various crosses between the Silky and the Brown Leghorn breeds. By 

 a happy accident we are able to adduce independent and cogent 

 evidence in favour of the interpretation which we have put forward. 

 In 1907 we bought a Silky ^^ which proved to be heterozygous for P 

 (i.e. Ppii). Mated with an Eg}'ptian hen, a brown bird with light 

 coloured shanks, he gave unpig merited as well as deeply pigmented hens. 

 Two of these unpigmented birds were mated back to the heterozygous 

 Silky f^ in 1908 and as was expected gave deeply pigmented and 

 unpigmented birds of both sexes, viz. 18 j/'j^ deeply pigmented, 15 <^ff 

 unpigmented, 21 %% deeply pigmented, 17 %% unpigmented. In 

 this way we were able to establish a strain of birds containing neither 



14-8 



