1 82 Sex-limited Inheritance [CH. 



skin of the bird has thus a deep purple or blue colour, due 

 to the black pigment showing through the uncoloured 

 epithelium of the skin*. Ordinary fowls, Brown Leghorns 

 for instance, the breed chiefly used in our work, have no 

 pigment in these parts beyond dubious traces in rare 

 exceptions. Such fowls we may call by contrast non- 

 pigmented, and the phenomena to be described occur as the 

 results of crossing them with Silkiest. 



The essential facts are as follows. When the Silky hen 

 is bred with Brown Leghorn cock all the F^ offspring, both 

 male and female, are either destitute of the pigmentation, or 

 only show a small amount of it in certain parts, especially 

 in the ribs, on the vertex of the skull, and on the iris. In 

 the case of the iris it shows in adult birds as minute dots 

 of black on the red ground. The skin of such F^ birds is 

 scarcely different from that of unpigmented breeds. Both 

 the skin and the periosteum sometimes have well-defined 

 patches of pigment. 



When however the Brown Leghorn hens are bred with 

 the Silky cock, the F l males are indistinguishable from 

 those bred in the reciprocal mating, but the F^ hens are 

 almost as much pigmented as the pure Silky hens. 



Of the many possible matings into which the F^ birds, 

 male or female, can be introduced, few have yet been made 

 on a scale sufficient to justify very confident statements. In 

 most of the derivative families thus produced there is also a 

 good deal of grading, and the analysis and classification of 

 these intermediate types have not yet been adequately 

 carried out. 



The main facts however are 



(i) That when the F l hens, whether of the deeply 

 pigmented sort or of the slightly pigmented kind formed in 

 the reciprocal mating, are bred with Brown Leghorn cocks, 

 their offspring, whether male or female, are never more 



* When the pigmentation occurs in birds having a yellow skin the 

 general appearance is greenish. White skin is dominant to yellow skin, 

 but the transmission of these characters is independent of that of the 

 peculiar pigmentation of the Silky. 



t The silkiness of the feathers is an ordinary recessive to the hard 

 plumage of common fowls. This character seems to be distributed inde- 

 pendently of the rest. 



