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VII. 
A THEORY OF BIRDS’ NESTS ; 
SHOWING THE RELATION OF CERTAIN DIFFERENCES OF 
COLOUR IN FEMALE BirDs, TO THEIR MODE OF 
NIDIFICATION. 
Tue habit of forming a more or less elaborate struc- 
ture for the reception of their eggs and young, must 
undoubtedly be looked upon as one of the most re- 
markable and interesting characteristics of the class of 
birds. In other classes of vertebrate animals, such 
structures are few and exceptional, and never attain 
to the same degree of completeness and beauty. Birds’ 
nests have, accordingly, attracted much attention, and 
have furnished one of the stock arguments to prove 
the existence of a blind but unerring instinct in the 
lower animals. The very general belief that every 
bird is enabled to build its nest, not by the ordinary 
faculties of observation, memory, and imitation, but 
by means of some innate and mysterious impulse, has 
had the bad effect of withdrawing attention from the 
very evident relation that exists between the struc- 
ture, habits, and intelligence of birds, and the kind of 
nests they construct. 
In the preceding essay I have detailed several of | 
these relations, and they teach us, that a consideration 
of the structure, the food, and other specialities of a 
