a 
A THEORY OF BIRDS’ NESTS. 257 
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 versa. 
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 at- 
tempted 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 
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