Until convincing evidence is forthcoming, the question is better left undecided. B. EVIDENCE FROM BIRDS. Probably a greater difference in the secondary sexual characters is shown in birds than in any other group. It is true that there are species, such as the doves and pigeons, in which the plumage of the male is much like that of the female, but this is the exception rather than the rule. At the other extreme are species like birds of paradise, hummingbirds, fowls, pheasants, ducks, and many passerines, in which the plumage of the two sexes is entirely different. Our knowledge as to the relation between the nuptial plumage of the male and the condition of the sex-organs rests largely on information gained by castration in poultry and ducks and on the assumption of the nuptial plumage in several species only at the mating season. John Hunter in 1780 described a pheasant with male plumage. His account of a similar change in a pea fowl is so complete that I venture to quote it in full: “Lady Tynte had a favorite pyed pea-hen, which had produced chickens eight several times; having moulted when she was about eleven years old, she astonished the lady and her family by showing the feathers peculiar to the other sex, and appearing like a pyed peacock. In this process the tail, which was similar to that of a cock, first appeared after moulting. In the following year she moulted again, and produced the same feathers. In the third year she did the same; at the same time she had spurs similar to those of a cock. She died in the following winter during the hard frost, namely, in the winter 1775-6. She never bred after this change in her plumage. This bird is now preserved in the Museum of Sir Ashton Lever.”[17] “From what has been related of these two birds, may it not reasonably be inferred that it seems probable that all those wild pheasants of the female sex, which are found with the feathers of the cock, had changed the nature of their feathers, particularly at a certain age? “If this idea be just, it shews that there is a disposition in the female to come nearer and nearer to the male, at least in the secondary properties; or it may rather be said that the female is later in producing this change than the male is; for it has already been observed that both sexes when young differ not from each other in these respects, but that the male appears to be the one that by degrees separates from the female in its secondary properties.”