RESULTS OF CASTRATION IN DUCKS. 39 



and reddish buff. Keel: dull slate with huffish streaks. Re- 

 mainder not conspicuously modified. Sex feathers absent. 



The female, so far as I have observed, undergoes no radical 

 change in coat color, though in one case, at least, the patterns of 

 the feathers were considerably different in August from those of 

 October. Compare Fig. 4, E with F; Fig. 6, D with F. 



As a result of the molt in early summer, both sexes of the adult 

 and the young are quite similar for a time. Its meaning is un- 

 certain. Newton ascribes the assumption of the summer plumage 

 by the drake to the loss of the power of flight temporarily, since 

 the remiges all fall out together. But in other cases where a 

 similar double molt occurs, the male retains the modified plumage 

 for several months; nor does he become incapable of flight. As 

 will be shown later, the presence of the active testis is necessary 

 for the drake to assume this plumage. Conditions in the mallard, 

 as far as I can find out, appear to be somewhat different from 

 the Rouen. The summer plumage seems to persist longer. The 

 one male in the American Museum in a transition stage, had a 

 brown edging to the feathers of regions, which, in the male 

 Rouen, have no such edging. 



Young. -When first hatched the young are brownish black 

 with a few yellowish stripes or spots. While they are acquiring 

 their first coat of feathers both sexes resemble the female in gen- 

 eral appearance. This summer, however, I found certain char- 

 acters of the plumage by which the sexes could be distinguished 

 at a very early age (Fig. 8, D, E, from birds about 7 weeks old). 

 The young "peep" for several weeks after hatching. The voice 

 of the young female is modified into that of the adult a few weeks 

 before that of the young drake. The latter is about four months 

 old when he takes on the adult plumage. At this time the 

 testes are still very small. 



Description of Feathers. 1 Male in breeding plumage. Head 

 and upper neck: distal half, metallic green; proximal half, dull 

 black with narrow white base; on the ventral side of head, this 

 base may be more extensive. Neck ring: entirely white. The 

 feathers of regions immediately adjoining the neck ring may be 

 many kinds of mixtures of white, red and black. Ventral surface. 



J The words distal and proximal refer to the feathers. 



