concealed. Much less can there be shown any group of birds, in which the females are all of decidedly conspicuous colours on the upper surface, and yet sit in open nests. The many cases in which birds of dull colours in both sexes make domed or concealed nests, do not, of course, affect this theory one way or the other; since its purpose is only to account for the fact, that brilliant females of brilliant males are always found to have covered or hidden nests, while obscure females of brilliant males almost always have open and exposed nests. The fact that all classes of nests occur with dull coloured birds in both sexes merely shows, as I have strongly maintained, that in most cases the character of the nest determines the colouration of the female, and not vice versâ.
If the views here advocated are correct, as to the various influences that have determined the specialities of every bird’s nest, and the general colouration of female birds, with their action and reaction on each other, we can hardly expect to find evidence more complete than that here set forth. Nature is such a tangled web of complex relations, that a series of correspondences running through hundreds of species, genera, and families, in every part of the system, can hardly fail to indicate a true casual connexion; and when, of the two factors in the problem, one can be shown to be dependent on the most deeply seated and the most stable facts of structure and conditions of life, while the other is a character universally admitted to be superficial and easily modified, there can be little doubt as to which is cause and which effect.
Various modes of Protection of Animals.
But the explanation of the phenomenon here attempted does not rest alone on the facts I have been able now to adduce. In the essay on “Mimicry,” it is shown how important a part the necessity for protection has played, in determining the external form and colouration, and sometimes even the internal structure of animals.