_Greater Brilliancy of some Female Birds._--There is one other very curious case of sexual colouring among birds--that, namely, in which the female is decidedly brighter or more strongly marked than the male; as in the fighting quails (_Turnix_), painted snipe (_Rhynchæa_), two species of phalarope (_Phalaropus_), and the common cassowary (_Casuarius galeatus_). In all these cases, it is known that the males take charge of and incubate the eggs, while the females are almost always larger and more pugnacious. In my “Theory of Birds’ Nests” (_Natural Selection_, p. 251), I imputed this difference of colour to the greater need for protection by the male bird while incubating; to which Mr. Darwin has objected that the difference is not sufficient, and is not always so distributed as to be most effective for this purpose; and he believes that it is due to reversed sexual selection, that is, to the female taking the usual _rôle_ of the male, and being chosen for her brighter tints. We have already seen reason for rejecting this latter theory in every case; and I also admit that Mr. Darwin’s criticism is sound, and that my theory of protection is, in this case, only partially, if at all, applicable. But the theory now advanced, of intensity of colour being due to general vital energy, is quite applicable; and the fact that the superiority of the female in this respect is quite exceptional, and is therefore probably not in any case of very ancient date, will account for the difference of colour thus produced being always very slight.