RESULTS OF CASTRATION IN DUCKS. 43 



types of feathers which the female lacks. Thus, the feathers 

 of the top of the head have no buff edges. Those of the posterior 

 keel region may have gray vermiculations on the margins. Those 

 of the throat and upper neck regions, however, appear to be 

 nearly identical with female feathers of the same sections. The 

 breast feathers present some complications. Certain types of 

 these are common to both sexes, but the male has certain forms 

 not possessed by the female. The differences, though elusive, 

 may perhaps be stated as follows : The apical part of the male's 

 breast feather is claret; that of the female is buff. There is a 

 tendency in the male for the red or buff bands to increase from 

 two to three and to become transverse. In the female the ten- 

 dency is for the bands to become reduced in number and to 

 become longitudinal. Only a statistical study could determine 

 just the exact relations between the two sexes. 



This discussion, I think, makes.it clear that the modifications 

 in the plumage of the male are, on the whole, of a type peculiar 

 to his sex. It can hardly be maintained that this is an example 

 of the assumption by the male of the female's plumage, especially 

 as I shall show later, the presence of the testis is necessary for 

 its appearance. The power to change his plumage is, indeed, a 

 sort of physiological secondary sexual character. 



Experiments. 



Thus far I have castrated 7 males and 5 females.^ Three 

 males and two females lived for considerable periods. No. 470^^ 

 and 49 were castrated in early spring, 1909, when a little less 

 than a year old. The right testis of No. 19c? was removed at 

 this same time, but the left was not removed till August 8. The 

 left testis of No. id^ (hatched spring 1908) was removed August 

 8, but owing to excessive bleeding, the right was well ligatured 

 and allowed to remain. These two males were in summer plu- 

 mage when operated on. No. 249 , 12 weeks old, was castrated 

 August 13. No. ic?. No. 249 and No. 49 are still alive. 



Results.— Males: No. 470 did not take on the summer plumage 

 in 1909. He was unfortunately killed by dogs in spring of 1910. 

 No. I molted in August, 1910, but did not take on the summer 



iNot including several others which died in tiic early part of the work. 



