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 6 Philosophy of 
Birds’ Nests 5 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-ooloured 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 . 1 
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 heron varies its site between trees, cliffs, and 
open fen . 2 Again, Audubon, in his 6 Ornithological Bio- 
graphy,’ gives many cases of conspicuous local variations 
in the nests of the same species in the northern and 
1 See Descent of Man , p. 452 et seq, 
2 See Newton, JSnoy* Brit art, 4 Birds, 5 
