A THEORY OF BIRDS’ NESTS. 261 
Darwin informs me he has facts to support), I impute 
the difference, in the great majority of cases, to the 
greater or less need of protection in the female sex in 
these groups of animals. 
This need was seen to exist a century ago by 
the Hon. Daines Barrington, who, in the article 
already quoted (see p. 220), after alluding to the 
fact that singing birds are all small, and suggesting 
(but I think erroneously) that this may have arisen 
from the difficulty larger birds would have in con- 
cealing themselves if they called the attention of 
their enemies by loud notes, goes on thus:—“I 
should rather conceive it is for the same reason no 
hen bird sings, because this talent would be still 
more dangerous during incubation, which may pos- 
sibly also account for the inferiority in point of 
plumage.” This is a curious anticipation of the 
main idea on which this essay is founded. It has 
been unnoticed for near a century, and my atten- 
tion was only recently called to it by Mr. Darwin 
himself. 
Conclusion. 
To some persons it will perhaps appear, that the 
causes to which I impute so much of the external 
aspect of nature are too simple, too insignificant, 
and too unimportant for such a mighty work. But 
I would ask them to consider, that the great object 
of all the peculiarities of animal structure is to pre- 
serve the life of the individual, and to maintain the 
existence of the species. Colour has hitherto been 
