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 Agricultural 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 plumage 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 the light for a week or two and meal-worms were added to the diet. This invariably resulted in a full resumption of song.