RELATING TO SECONDARY SEXUAL CHARACTERS. 81 



Throughout the greater part of the year the Rouen drake has the 

 nuptial plumage. The head is green and the breast is claret. Two 

 median tail feathers are strongly curved; the next two are also often 

 curved. These four are called the sex feathers. At the close of the 

 breeding-season (July) both sexes molt. The male now has the same 

 coat as the female, or nearly so. The green head becomes brown to buff ; 

 the sex feathers are straight. The change back again to the nuptial 

 plumage begins at the end of summer and is completed early in October. 

 Thus in the race of Rouens the eclipse plumage lasts only a very short 

 time. In the mallard it lasts longer. The eclipse plumage develops, 

 therefore, only when the testes are active, or, as Goodale puts it, "the 

 presence of the active testis is necessary for the drake to assume this 

 plumage." Conversely, the nuptial plumage comes on in the late 

 summer, when mating is over, and when the testes have shrunken and 

 are not active, at least as far as the sex-cells are concerned. In some 

 respects the situation is like that in the fowls, for in both the testes are 

 not necessary for the development of the full plumage, but in other 

 respects the situation is different, because at the time in the ducks 

 when the testes are active the eclipse plumage develops. Are we to 

 suppose that at the time of sexual activity a substance is produced 

 analogous to that produced by the ovary of the female? This seems 

 the most plausible assumption, for we know that if the testis is removed 

 the eclipse plumage does not appear. Such a situation suggests a 

 comparison with the Sebright, where it has been shown that the testis 

 must actively produce some substance which, like that in the ovary, 

 keeps down cock-feathering. It is plausible, even if it can not be 

 established, that the substance in the duck and the inhibitory substance 

 in the male Sebright are the same as that produced in the female. 



Goodale's results with females (ducks) are not so clear cut, because 

 the ovariotomized females turned out to be of two sorts. One sort is 

 almost identical with the male, the other is more intermediate. There 

 are sufficient reasons for thinking, he says, that these differences are 

 not due to defective operations. Goodale suggests a genetic difference 

 in the females used, but this is apparently even to Goodale himself 

 not a very satisfactory solution. For our present purpose the impor- 

 tant fact is that the ovariotomized female may assume the perfect male 

 plumage. Evidently the ovary produces some substance which, as in 

 the hen, suppresses the potential plumage of the male. One such female 

 known to have had all the ovary removed never assumed the summer 

 (eclipse) plumage of the drake. On the other hand, another female 

 developed first the nuptial plumage, but this was replaced by the 

 summer coat "of the male of this variety." Again, in the summers of 

 1914 and 1915 the change to the eclipse plumage was followed in the 

 autumn by a return to the nuptial plumage. 



