BIRDS— NIDIFICATION. 299 



much reason to anticipate that the nest of the little crus- 

 tacean Podocerus, or the cell of the hive-bee, is constructed 

 by a process of conscious imitation, as that this is the case 

 with the nests of birds. And this theory is not well sub- 

 stantiated by facts because, if the theory were true, we 

 should expect considerable differences to be usually pre- 

 sented by nests of the same species. Unless the con- 

 struction of the nest of any given species were regulated 

 by a common instinct, numberless idiosyncratic peculi- 

 arities would necessarily require to arise, and there would 

 only be a very general uniformity of type presented by the 

 nests of the same species. 



A more valuable contribution to the ' Philosophy of 

 Birds' Nests ' is furnished by this able naturalist when he 

 directs attention to a certain general correlation between 

 the form of the nest and the colour of the female. For, 

 on reviewing the birds of the world, he certainly makes 

 good the proposition that, as a general rule, liable however 

 to frequent exceptions, dull-coloured females sit on open 

 nests, while those that are conspicuously coloured sit in 

 domed nests. But Mr. Darwin, in a careful review of all 

 the evidence, clearly shows that this interesting fact is to 

 be attributed, not, as Mr. Wallace supposed, to the colour of 

 the female having been determined through natural selection 

 by the form of the nest, but to the reverse process of the 

 form of the nest having been determined by the colour of 

 the female.^ 



Another general fact of interest connected with nidifica- 

 tion must not be omitted. This is that the instincts of 

 nidification, although not so variable as the theory of Mr. 

 Wallace would require, are nevertheless highly plastic. 

 The falcon, which usually builds on a cliff, has been 

 known to lay its eggs on the ground in a marsh ; the 

 golden eagle sometimes builds in trees or on the ground ; 

 while the hercm varies its site between trees, cliffs, and 

 open fen.2 Again, Audubon, in his * Ornithological Bio- 

 graphy,' gives many cases of conspicuous local variations 

 in the nests of the same species in the northern and 



^ See Descent of Man, p. 452 et seq. 



■ 8ue Newton, Enoy. Brit., art. ' Birds.' 



