A THEORY OF BIRDS' NESTS. 257 



females of brilliant males are always fou'.id 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 



