ON SOMATIC SEX-CHARACTERS 81 



almost completely disappear after the breeding 

 season and reappear in the following season. In the 

 interval the drake passes into a condition of plumage 

 in which he resembles the female ; and this condition 

 is known as ' eclipse.' The male plumage, therefore, 

 in the drake has a history somewhat similar to that of 

 the antlers in deer. Two investigations of the effects 

 of castration on ducks and drakes have been recorded. 

 H. D. Goodale ^ removed the generative organs from 

 both drakes and ducks of the Rouen breed, which 

 is strongly dimorphic in plumage. One drake was 

 castrated in the early spring of 1909 when a little less 

 than a year old. This bird did not assume the 

 summer plumage in 1909, that is, did not pass into 

 eclipse. It was in the nuptial plumage when 

 castrated. This breeding or nuptial plumage is well 

 known : it includes a white neck-ring, brilliant green 

 feathers on the head, much claret on the breast, 

 brilliant metallic blue on the wing, and two or more 

 upward curled feathers on the tail. The drake 

 mentioned above was accidentally killed in the 

 spring of 1910. Another drake was castrated on 

 August 8, 1909 : only the left testis was removed, 

 the other being ligatured. At this time the bird 

 would be in eclipse plumage. It appears from the 

 description that it assumed the nuptial plumage in 

 the winter of 1909, and did not pass into eclipse 

 again in the summer of 1910. Thus in drakes the 

 effect of castration is that the secondary sexual 

 character remains permanently instead of being 

 lost and renewed annually. Goodale, however, does 

 not describe the moults in detail. In the natural 



* 'Castration of Drakes.' Biol. Bulletin^ Wood's Hole, Mass., vol. xx., 

 1910. 



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