INHERITANCE OF PARTICULAR CHARACTERISTICS. 73 



These results are peculiar. If both normal-toed and extra-toed ancestors 

 were heterozygous in respect to toes, we should expect the result obtained in 

 Fj. It is quite possible, though not probable, that this is true. Then extra 

 toe would be dominant, although sometimes so imperfectly so as not to 

 appear. In F 2 the parents were normal-toed, either because "normal" is 

 recessive or because it is imperfectly dominant. All offspring should be 

 normal-toed in the one case or give 100 per cent to 75 per cent extra-toed 

 in the other. The result is not in accordance with either hypothesis. If 

 there is any dominance in this generation it is of the normal toe. Bateson 

 and Saunders (1902, p. 124), while concluding that extra toe is dominant, 

 find "that the recessive foot character may sometimes dominate." Hurst 

 (1905, p. 150) also got, in a cross between Leghorn and Houdau, some 

 normal-toed offspring which, interbred, produced extra-toed progeny. He 

 concludes that a usually dominant character may recede in certain individ- 

 uals. There is danger here of straining Mendel's law. It is better to hold 

 ' ' explanations ' ' in abeyance until the matter of inheritance of polydactylism 

 has been more thoroughly investigated. Certainly the facts of inheritance 

 of polydactylism in man can hardly be explained on Mendelian principles 

 (Davenport, 1904). Polydactylism is at least not recessive. The new, posi- 

 tive, pathological characteristic holds its own against the older one. 



SKIN COLOR. 



The epidermis of poultry is everywhere covered by feathers except on the 

 beak, face, and feet. The naked portions may, however, have a different 

 color from the covered ones ; consequently the correlation between general 

 skin, beak, and foot color, although not absent, is not close. Thus, although 

 the yellow beak and foot of the Leghorn are correlated with its yellow skin, 

 the black legs and beak of the Black Minorca are not accompanied by a 

 black skin. Not all exposed parts, even of the skin, are of one color, for the 

 face, at least, maybe red or white when the legs are black. Color of beak 

 and foot are, on the other hand, closely correlated, individual variations of 

 the one being usually associated with corresponding variations of the other. 

 This correlation is doubtless the result of the similar cornification of the skin 

 of beak and foot, whereas (excepting races with opaque white face) the 

 vascular face and earlobes are white or red, according to a less or greater 

 blood supply in them. 



The pigmentation of the epidermis of poultry falls into three classes : (a) 

 Without pigment or white ; (U) yellow ; (c) black. White skin is the com- 

 monest, even among poultry with black plumage and feet. Yellow skin is 

 found in the Asiatics, derived from the Aseel- Malay ancestry, and is a char- 

 acteristic of the White Leghorn. Black pigment occurs in the skin of the 

 Silky fowl and the Negro fowl. Black pigment is to be regarded as a new 

 variant and of the nature of a pathological sport melanism. When black 



