230 THE BIOLOGY OF BIRDS 



have started to grow the hormone is not always able to check 

 them. 



Castrated ducks of both sexes showed no change of 

 voice, but castrated fowls are disinclined to give utterance to 

 any kind of sound. Capons can utter all the sounds of which 

 the cock is capable, but they rarely do so. 



As far as Goodale's experiments went, with one exception, 

 the operations left the moult of the capon uninfluenced, but 

 castrated drakes lose the power of developing the summer 

 plumage. The colour of the drake's mandible was un- 

 affected, but in the duck certain pigments disappeared. 

 The behaviour of castrates is on the whole negative as com- 

 pared with normal adults ; it corresponds rather closely 

 to that of young birds shortly before they become mature. 

 The birds eat, drink, and move about rather quietly. 



It seems clear that while some secondary sex-characters 

 are absolutely dependent on the internal secretion of the 

 gonad, such as the comb, others are more or less independent, 

 such as the spurs. 



If the testes of the bird be removed, the majority of the 

 secondary sex- characters develop, though a few may remain 

 in an infantile condition. Thus " hen-feathered " males 

 illustrate juvenile, rather than female characters of plumage. 



If the ovary of a domestic bird be removed completely, 

 many of the secondary sex-characters of the male appear, 

 and always of the male of the same race. Some castrated 

 ducks become nearly complete replicas of the male, others 

 are imperfect imitations. But it is not to be supposed that 

 the female is a suppressed hermaphrodite, it is rather that 

 the male characteristics are latent, and that they find ex- 

 pression on the removal of the ovary, the hormone of which 

 normally keeps them inhibited. 



As an abnormal occurrence there is a certain amount of 

 hermaphroditism in birds. A number of cases in fowls, 

 where females with embryonic or degenerating ovary showed 

 some development of testes, as well as external masculine 

 characters, have been described by Alice M. Boring and 

 Raymond Pearl (191 8). There is no structural counterpart 



