Amorousness, then, is the dominant feature of the males among all animals: and this sex presents yet another characteristic which is to be borne in mind. In all that concerns the evolution of ornamental characters the male leads. In him we can trace the trend which evolution is taking; the female and young afford us the measure of the advance along the new line which has been taken. Why this should be is inexplicable. But sooner or later the females assume, or will assume, all the features originally possessed by their lords; and finally the young also follow suit. That is to say, the females and young tend to retain the ancestral characters. In the course of time the ability to develop new features by the male loses its impetus, and not till then, apparently, do the females, and still later, the young, begin to share his glory. These remarkable features are strikingly illustrated among the birds, as these pages will show. Nature is nothing, if not perverse. And hence it happens that there are many exceptions to every rule which one formulates. Among the birds, for example, there are species wherein the rule that the female follows her mate in the acquisition of new characters is, so to speak, set aside. She follows a line of her own. This is true, at any rate, of superficial characters, such as coloration. By some curious change in her “metabolism,” as the conversion into living tissue of the substances taken as food is called, this coloration may attain a brilliance in no way inferior to that of the male, but strikingly different. The beautiful Orange Fruit-pigeon (_Chrysoenas victor_) furnishes a case in point, the male being of a gorgeous orange-yellow, the female of a no less vivid green. But the differences are not so great as they appear at first sight. For the male was originally green, and the female has thus but intensified the ancestral livery. Green, it should be remarked, of a more or less olive shade, always precedes yellow in development; and yellow may yield to red, but this order is never reversed. A no less striking case is that of the Upland Goose (_Cloephaga magellanica_), the male of which is pure white, while the female wears a livery of chestnut and brown. But so sharply are the colours defined that it would be difficult to say that one was of a higher order of coloration than the other. To what causes or factors are these departures due?