46 MENDELISM AND 



pigeons have been derived from C. livia, and of fowls 

 from G. bankiva, is too strong to be disregarded 

 because it does not agree with theoretical con- 

 ceptions. 



My own experiments in crossing Silky fowls with 

 Gallus bankiva (P.Z.S., 1919) show that the re- 

 cessive is not always pure, that segregation is not 

 in all cases complete. The colour of the bankiva 

 is what is called black-red, these being probably 

 the actual pigments present, mixed in some parts 

 of the plumage, in separate areas in other parts : 

 the Silky is white. There are seven pah's of char- 

 acters altogether in which the S,ilky differs from 

 the bankiva. Both the pigmented skin of the 

 Silky and the colour in the plumage of the bankiva 

 are dominant, so that all the offspring in F 1 or the 

 first generation are coloured fowls with pigmented 

 skins. But in later generations I found that with 

 regard to skin pigment there were no pure recessives. 

 Since the heterozygote in F^ was deeply pigmented, 

 it is certain that a bird with only a small amount 

 of pigment in its skin was a recessive resulting from 

 incomplete segregation of the pigmented character. 

 The pigment occurred chiefly in the skin of the 

 abdomen and round the eyes, and also in the 

 peritoneum and in the connective tissue of the 

 abdominal wall. It varied in different individuals, 

 but in some, at any rate, was greater in later genera- 

 tions than in the earlier. The condition bred true, 

 as pure recessives do ; and when such an impure 

 recessive was mated with a heterozygote with 

 black skin, the offspring were half pigmented 

 and half recessive, with some pigment on the 

 abdomen of the latter. 



