40 GONADECTOMY IN RELATION TO THE SECONDARY 



Rouen undergoes the following molts: Sometimes in early summer, 

 usually in June and July, the actual date varying a great deal with 

 different individuals, each sex molts, the new coat of the male forming 

 the so-called summer plumage, while that of the female is not very 

 different from that worn during the breeding plumage. Early in the 

 fall each sex molts again, the male this time resuming his breeding 

 plumage. The flights, however, are only molted once. Thus, there 

 is an interval of 3 or 4 months during the summer when each sex is in 

 a state of almost continuous molt in some part or other of the body. 

 For the other 8 or 9 months the birds ordinarily retain the coat devel- 

 oped in the fall, i. e., the breeding plumage. But the castrated indi- 

 viduals of each sex molt at irregular intervals throughout the year. 

 The molt is extensive in that it includes nearly all the feathers except 

 those of the wing. The new plumage is like the one that preceded it, 

 except in the case of those females that have assumed the summer 

 plumage of the male. 



Castration of the drake has a remarkable influence on the summer 

 molt. During the same period of the year that the normal drake is 

 taking on the summer plumage, the castrated individuals molt, but do 

 not assume the summer plumage. Instead, the new feathers are like 

 the old. This is clear evidence that the testes control the characters 

 of the summer coat. This coat imitates that of the female, but does 

 not duplicate it, though feathers in certain regions of some males are 

 indistinguishable from those of the female. Perhaps an explanation of 

 this relation can be found in the following considerations : The summer 

 plumage begins to develop when the breeding-season is at its height 

 i. e., at the time of the greatest sexual activity or at least soon after 

 it has reached its climax, usually in June or early July. During this 

 period the males are most active hi treading the females and naturally 

 the testes are at the period of greatest activity. The so-called breed- 

 ing plumage, however, develops in early autumn, after the breeding 

 season is over, when the males are least active and when the testes are 

 in a state of comparative repose. The changes may or may not be 

 connected with the greater production of spermatozoa at this season of 

 the year, but may be dependent on some other physiological change in 

 the testes. An attempt will be made to test this hypothesis by pulling 

 feathers during the breeding season, some months ahead of the normal 

 molt, on the assumption that the state of eclipse is due to changes in the 

 testes resulting from their activity. 1 



Although it is perfectly clear that following castration the drake 

 may not assume the summer plumage, it is not yet certain that com- 

 plete castration in the sense of removal of both the spermatogenic por- 

 tion and efferent ducts (epididymis) is necessary for this result. 



x The experiment was tried in the spring of 1916, with results agreeing with the hypothesis 

 proposed. 



