SEXUAL CHARACTERS OF SOME DOMESTIC BIRDS. 35 



the breast and belly. In the belly region the markings of the feathers 

 in both the castrated female and the male in summer plumage are 

 vague, but usually show a certain amount of vermiculation. The 

 feathers of the breast regions in each of the three plumages (breeding 

 male, summer male, and female), however, have a distinct pattern, 

 which is often very varied and exceedingly difficult to describe briefly. 

 In the female, the feathers are brown, penciled concentrically with buff 

 or else more or less spotted (cf. plate vi, figs, m and o). In the male 

 they are self-colored claret. In the summer plumage of the male they 

 are again distinct, having a reddish tip, the remainder being buff and 

 brown, but with at least one or two transverse bars (cf. plate vi, figs, r 

 and q). In the castrated female the feathers of this region approach 

 most closely to the latter type. The transverse buff or reddish-buff bars 

 are characteristic of the summer plumage of the male and of Type II 

 females. Certainly they bear no resemblance to the plumage of either 

 the breeding male or female. In the head region of the castrated 

 females a mosaic is usually formed, part of the feathers being distinctly 

 male, the other of a nondescript semi-female character. The remainder 

 of the dorsal region is always approximately male, except for some of 

 the scapulars. 



Why so many of the castrated females should develop a plumage 

 that in part is very much like the summer plumage of the male is not 

 at all clear. It can not be due to the absence of all gonads, as recorded 

 above, for in the male the absence of such gonads results in a failure of 

 the male to assume the summer plumage. Moreover, this plumage is 

 not characteristic of all castrated females, since some develop the 

 entire male breeding plumage. It would seem more likely that the 

 plumage of Type II is the result of some peculiarity in the gametic con- 

 stitution of the bird. 



Possibly an explanation of this peculiar behavior may be found in 

 the following suggestions : In poultry breeding, what is known as the 

 double-mating system is used to secure individuals which come nearest 

 to the standard requirements. The term " double mating" means 

 simply that two separate lines are used to secure the standard male and 

 female respectively. The female from the standard male line and the 

 male from the standard female line are wasters. In the last analysis, it 

 means that to get a pair of show-room birds the females are bred from 

 one strain, the males from another, each strain being carefully bred by 

 itself. In Rouen ducks the breeder endeavors to produce a female with 

 clean-cut concentric penciling of the type shown in plate vi, o. The 

 male of the female line, though without penciling in the adult plumage, 

 often has well-developed penciling in the juvenile or summer plumage, 

 and, other things being equal, those males having the best penciling 

 are chosen as breeders for standard females. 



Under such selection it follows that the flock as a whole is held reason- 

 ably close to one end of the curve of variation. In the cross-breds the 



