46 INTERNAL SECRETIONS 



castration, but at the summer moult does not acquire the 

 characteristic summer plumage.^ If the removal of the sexual 

 glands is incomplete the female duck preserves the female 

 plumage, whereas the drake continues to assume the summer 

 plumage, The voices of castrated ducks of both sexes under- 

 went no changes (with one exception noted above). Sexual 

 behaviour was lacking. The penis was found sometimes 

 rather smaller and more flaccid than normally, but otherwise 

 essentially the same. In experiments undertaken some years 

 previously Poll observed castrated adult drakes assume the 

 summer plumage ; there can scarcely be a doubt that the result 

 was due to incomplete castration ; Goodale stated that in 

 those cases in which the castrated drake assumed the summer 

 plumage, remains of the testicle were to be found. Zawadowsky 

 (1922) has confirmed the statements of Goodale and Pezard 

 in domestic fowls, pheasants and ducks. 



Theoretical. 



We have seen that castration leads in mammals, not to an 

 assumption of the other sex, but to a common form in which 

 some of the sexual characters are absent. The sexual differ- 

 ences in birds are intelligible in the same kind of way. The 

 castrated cock and hen are very similar in their external appear- 

 ance; so also are the castrated drake and duck. It is true 

 that some of the results of castration in female birds might 

 be interpreted as due to an assumption of characters of 

 the male type. But the castrated hen does not show the 

 sexual behaviour of the cock, and a male head apparel is not 

 assumed. Thus the facts justify the suggestion that the cock 

 and the hen converge after castration to a common sexual type 

 which is externally more like the male than the female form. 

 It is possible to hold the view that the plumage and the spurs of 

 the cock, or the plumage of the drake are characters which 

 developed in a common asexual embryonic soma without 

 being influenced, excepting possibly very slightly, by the male 



1 The moult of ducks and drakes takes place in summer, as a rule in June 

 and July. The drake assumes at this time its special summer plumage. In 

 the early autumn male and female moult a second time. The drake now 

 loses its summer plumage, which is thus worn only a few months. After 

 castration the moult becomes irregular. 



