84 THE GENETIC AND THE OPERATIVE EVIDENCE 



present in the Sebright. The normal allelomorph in question need 

 not have had any relation to the other complex; in fact, it seems not 

 to have any, because the castrated Sebright (with both normal allelo- 

 morphs replaced by genes for hen-feathering) still develops the charac- 

 teristic cock-feathering. 



The outcome in the duck with its double male plumage is still more 

 puzzling when we attempt to analyze the situation in the light of the 

 selection theory. At the height of the breeding-season, when his testes 

 are enlarged and functioning actively, a substance is being produced 

 that leads to the eclipse of the nuptial plumage. If the male were 

 selected by his partner for his plumage, he would be chosen for a 

 plumage that develops in the absence of the functioning testes. If the 

 male is chosen because of his greater aggressiveness or "activity" or 

 "vitality" due to the development of his testes, the result would be to 

 select males that would probably develop a better eclipse plumage. 

 The case is interesting because it gives an opportunity to distinguish 

 between a plumage that develops under the influence of the sexual 

 organs and one that does not; and the latter is paradoxically the 

 nuptial plumage. It is true that the male might be selected for his 

 nuptial suit, and, theoretically at least, female choice might still be 

 made responsible for this plumage, but this merely shifts the problem, 

 for it leaves "unexplained" the appearance historically of the effect of 

 the activity of the testes in suppressing this plumage for a short time 

 after maturity. No doubt an attempt might be made to show that 

 natural selection comes in at this time of the year in giving a protective 

 color to the male, but so long as any evidence is lacking as to the need 

 of this protection the argument serves rather to further complicate an 

 already difficult situation. 



Goodale has written to me that there is an account, in the Agricul- 

 tural Journal, Union of South Africa, iv, 1912, of the effects of the 

 removal of the ovary of the female ostrich. I have not been able to see 

 the account, but according to my informant such female individuals 

 assume the male secondary characters. 



Of unusual interest in connection with the seasonal change of plum- 

 age in males of dimorphic species are Beebe's experiments with scarlet 

 tanagers and bobolinks. In both species the males in their nuptial 

 plumage are very different from the females. Full-plumaged males of 

 both species, at the height of their "vocal and physical condition," 

 were confined in small cages. The supply of light was gradually cut 

 off and a slight increase of the amount of food was allowed them. The 

 birds became less active in consequence and increased in weight. ' The 

 time for the fall molt came and passed and not a single feather was 

 shed." The birds had skipped the autumn molt and remained in their 

 nuptial plumage. The song soon died away ; "the birds seldom uttered 

 even a chirp." From time to time a bird was gradually brought into 



