A FEMINIZED COCKEREL 427 



while castration of the male does not alter the plumage. In 

 other words, the secondary sexual difference of the birds thus 

 far studied can be largely explained on the assumption that an 

 internal secretion of the ovary is responsible for the differences 

 observed. All the differences, however, cannot be explained 

 thus. The size of the comb and wattles in the male depends 

 upon the testes but in the female the relation to the gonads is 

 more complicated. The comb of the young pullet as a rule 

 remains small until about the time egg production begins, when 

 it enlarges rapidly to adult size. With the cessation of laying, 

 the comb shrinks, often to half its former size, but enlarges some- 

 what with the resumption of laying, though it does not often 

 reach its former size, at least in Leghorns. In old Leghorns, the 

 comb often remains shrunken throughout the laying season. 

 In some castrated females, the comb becomes very large and 

 cock-like, while in others it has remained small. The spurs 

 appear to be independent of any influence of the testes since 

 they develop well in the capon. The ovary appears to exert 

 an inhibitory effect on the development of the spurs, since all 

 castrated females develop spurs. The inhibition may or may 

 not be complete because in certain strains spurs frequently 

 appear on the females, though almost completely absent in other 

 strains. It is possible that the secretion of the ovary is complex, 

 one constituent controlling the spurs or the shape of plumage, 

 another the color, etc. Or, it may be that the general growth 

 potentialities are greater in some individuals than ^' others, so 

 that characters such as spurs escape from the inhibitc influence 

 of the ovary. The vocal organs and behavior of the birds are 

 also somewhat independent of the sexual organs. Capons fre- 

 quently crow and sometimes tread the hens. They also brood 

 the chicks. On the other hand, none of the castrated females, 

 even those that develop the habit of the males most perfectly, 

 have ever been seen or even suspected of crowing, nor as far as 

 known do they ever tread the hens, although special attempts 

 have been made with this end in view. 



It is evident, I think, that the difference between the secondary 

 sexual characters of the sexes cannot be ascribed solely to the 



