thing, though here—and this is significant—the difference, as well as the actual colour, is less striking. These varying degrees of brilliancy of colouring in this particular region, as between the mature and immature form, must surely have some meaning, and as it goes hand-in-hand with a similar, if not, as I believe, an identical difference in the hue of the naked facial integument, as well as with the pattern and shade of the plumage, I feel persuaded that all three are governed by the same general law.
As explained by Darwin—and nothing better, that I can see, than opposition has ever been opposed to his views—the beauty of certain birds has been acquired through the principle of sexual selection, and the lesser degree of it, which we notice in the young, represents the earlier and less-finished beauty of the adult in times gone by. Of all the elements which go to make up the beauty thus acquired, colour, on the whole, plays the most conspicuous part, and nothing can be more brilliant and striking than some of the colours that I am here speaking of. The only reason, therefore, why, in their use, and the laws that have governed their acquirement, they should be thought to differ from the hues and tintings of the plumage, or of the naked outer skin—the cere or the labial region—would be their habitual, necessary concealment. If, then, it can be shown that, far from their being always concealed, they are prominently displayed during the breeding season by certain birds which possess them in a marked degree, then, as far as
