RESULTS OF CASTRATION IN DUCKS. 4/ 



is the more common. Its transverse buff bands recall those of 

 the young male. The new feathers around the vent and sides 

 of body posterior to wings (Fig. 8, G, F) are largely of the male 

 breeding plumage type, though those of the sides are somewhat 

 darker, more like the feathers of the same place in summer 

 plumage. The new laterals are of the male summer type. Con- 

 ditions in the breast region are rather complex. The upper part 

 as a whole, is a deep claret, gradually becoming lighter ventrally 

 and shading into the keel region. There is no sharp boundary 

 as in the male. A feather from the upper (anterior) region is 

 shown in Fig. 4, L. Further down on the breast, types like that 

 shown in Fig. 4, K, are very common. The types shown in Fig. 

 4, B, Fig. 5, /, and Fig. 6, G, also occur, the last being especially 

 frequent at the sides. 



This female evidently is still undergoing modifications and in 

 due course of time may assume the complete plumage of the 

 male. At present she has the following distinctively male char- 

 acters. Brilliantly green feathers on head; white neck ring; 

 much claret in breast and some feathers indistinguishable from 

 the male's; numerous vermiculated feathers, often identical with 

 those of the male; rump feathers like that of male; and sex 

 feathers. I have not seen feathers like those shown in Fig. 5, 

 H, I; Fig. 6, G, in either normal sex, though feathers suggesting 

 the last have been seen in the male. The few feathers of purely 

 female type remaining are in the head and upper surface of 

 wing. The color of the bill has not changed. The voice, too, 

 is still the female's, though it has a tendency to break. 



All that can be said in regard to sexual behavior is that the 

 castrated females seem quieter than the others. Fuller obser- 

 vations will be made when the breeding instincts of both sexes 

 become more active. 



While the difference in plumage between these females may 

 be due to the difference in age when castrated, no discussion of 

 this point will be attempted in the present paper. 



Discussion. — The results of these experiments show that re- 

 moval of the testes does not bring about the assumption of the 

 female characters, but at most results in the loss of a male char- 

 acter. The loss of the power of taking on the summer plumage 



