W. Bateson and R. C. Punnett 203 



suggesting that this is not necessarily the case for all light-shanked 

 birds. An example may serve to illustrate our meaning. During 

 1908 and 1909 the fully pigmented F., ^ mentioned on p. 197 was 

 crossed with a Brown Leghorn $ and gave a typical result, viz. slightly 

 pigmented ^^ and fully pigmented % %. During both of these seasons 

 he was also run with a light-shanked % belonging to our recessive 

 white strain'. With her he gave 19 male chicks varying from slight 

 to moderate pigmentation, but of the 18 female cliicks 8 were fully 

 pigmented and 10 showed only a slight to moderate amount of pigment 

 (1908-9, Pen 24, 53). From this and other similar experiments it 

 seems natural to infer that some light-shanked hens may carry other 

 factors capable of modifying the Silky pigmentation besides that which 

 we have been able to demonstrate in the Brown Leghorn. 



Lastly we may refer to a cross which we made between our original 

 Silky cock and a hen which was homozygous for the dominant white 

 factor (1907, Pen IS, 397). All the offspring (18 ^^ and 22 ? $) 

 showed some pigment, sometimes a good deal, and this as a rule was 

 distributed in small irregular patches, but we were unable to notice 

 any difference between the two sexes. We think it not unlikely that 

 the hen used was potentially a dark-shanked bird, and that the 

 offspring of both sexes would have exhibited full pigmentation had not 

 its development been in some way checked by the dominant white 

 factor. The results however were complex and lack of opportunity 

 prevented us from following up the cross, but we have thought it worth 

 placing these cases on record since they indicate that radical differences 

 in constitution may exist among light-shanked birds, and that the 

 behaviour of our strain of Brown Leghorns with regard to the Silky 

 pigmentation is not necessarily typical of birds with unpigtnented 

 shanks. 



1 An account of the origin of this strain will be found in Reports to the Evolution 

 Committee of the Royal Society, in. p. 19, iv. p. 28. 



