RESULTS OF CASTRATION 47 



sexual glands ; and further that the development of the sexual 

 characters in the asexual embryonic soma may be influenced 

 very considerably by the female gonad. Pezard {1917, 1918) 

 points out that one can distinguish two different groups of 

 sexual characters; those the development of which depends 

 upon the sexual gland, and those which develop independently 

 of the latter. The comb, wattles, barbies, and voice in the 

 cock, and the sexual behaviour, are characters of the first kind, 

 while the plumage and the spurs belong to the second. On the 

 other hand, the plumage of the hen belongs to the first group, 

 as it results, in the hen, from the influence of the sexual gland 

 on the asexual type of plumage. The same point is mentioned 

 by Goodale (1916, p. 46): *'It is apparent," he says, "that the 

 inherited base for the secondary sexual characters in each 

 sex is the same," and that "the genetic factors that are trans- 

 mitted, if expressed in terms of their somatic results in the 

 absence of the ovary, are the male characters." The somatic 

 basis common to both sexes is influenced and changed by the 

 sexual glands. 



As is shown especially by Goodale in the case of drakes, the 

 plumage also of the male depends to a certain degree upon the 

 sexual glands ; the castrated drake does not assume the summer 

 plumage. By analogy one might suggest that all the character- 

 istic changes which occur in the plumage and in the sexual 

 behaviour of the male bird during heat are caused by changes 

 in the male sexual gland. In the domestic fowl the male 

 plumage does not show this dependence upon the male sexual 

 gland. But, nevertheless, there are a few feathers which in 

 the capon are longer than in the normal cock. The experi- 

 ments of Morgan made on the Sebright breed are of great 

 interest here. In the Sebright the cock and the hen have a 

 more or less similar plumage, the plumage of the cock being 

 like that of the hen. Morgan (1915, 1919) states that the 

 Sebright cock assumes after castration a plumage which is Hke 

 that of our domestic cock {Figs. 34A, 34B). Similar 

 observations were made by Morgan (1920 a) on hen- 

 feathered Campines, castrated at an age of 3J months. 

 After the experiments recorded by Morgan there can be 

 no doubt that in the Sebright cock the testicle influences 

 the development of the plumage in the same kind of 

 way as the ovary does. It may be that the same is 



