146 GENETICS AND EUGENICS 



but even pure bred birds may develop an occasional colored 

 feather, and in crosses with brown Leghorns, which have the 

 ancestral color, the heterozygotes produced may show traces 

 of color, as for example a reddish breast. A form of white 

 plumage genetically distinct from the foregoing is found in 

 white silky fowls and in some other breeds. In this the down 

 plumage is colored and the adult plumage is not as clear and 

 pure a white as that of white Leghorns. When such recessive 

 whites are crossed with white Leghorns, fully colored offspring 

 result in F2 though not in Fi. It is probable that recessive 

 white is not an extreme form of white spotting, as perhaps 

 the white of Leghorns is, but that it is due rather to some 

 change which produces fainter pigmentation ; to a loss varia- 

 tion, rather than to an inhibition. It is accordingly com- 

 parable with the albino or the pink-eye variation of rodents, 

 whereas the white of Leghorns is comparable with the black- 

 eyed white variation of rodents, an extreme form of white 

 spotting. Bateson has shown that there are two or possibly 

 three distinct classes of recessive white varieties, probably of 

 independent origin, for when two of these (one being the 

 white silky) were crossed, fully colored Fi offspring were ob- 

 tained similar in appearance to the wild Gallus hankiva. 

 This is a result comparable with that obtained when pink- 

 eyed rodents are crossed with albinos producing fully colored 

 young. It shows that white plumage in fowls, like pink eyes 

 and pale coats in rodents, may result from different genetic 

 changes. Pigment formation is a complex chemical process 

 in which several factors are concerned. Change in any one 

 of these may interfere with the normal pigmentation. 



It seems doubtful whether the Gallus hankiva pattern is 

 lost in the ordinary black breeds of fowls; more probably it 

 is simply covered up by an excessive development of black 

 pigment. Indeed in some cases the pattern is faintly visible 

 in the black breed and can readily be brought out in crosses. 

 Such varieties are comparable with the blackened agouti va- 

 rieties of some rodents (black squirrels for example) . In self 

 yellow (red or buff) breeds, the pattern fails to develop 



