A THEORY OF BIRDS’ NESTS. 247 
way in which nature works, and give us any insight 
into the causes which have brought about the marvel- 
lous variety, and beauty, and harmony of living things? 
I believe we can answer these questions in the affirm- 
ative; and I may mention, as a sufficient proof that 
these are not isolated facts, that I was first led to 
see their relation to each other by the study of an 
analogous though distinct set of phenomena among in- 
sects, that of protective resemblance and “ mimicry.” 
On considering this remarkable series of correspond- 
ing facts, the first thing we are taught by them seems 
to be, that there is no incapacity in the female sex 
among birds, to receive the same bright hues and 
strongly contrasted tints with which their partners are 
so often decorated, since whenever they are protected 
and concealed during the period of incubation they 
are similarly adorned. The fair inference is, that it is 
chiefly due to the absence of protection or concealment 
during this important epoch, that gay and conspicuous 
tints are withheld or left undeveloped. The mode in 
which this has been effected is very intelligible, if we 
admit the action of natural and sexual selection. It 
would appear from the numerous cases in which both 
sexes are adorned with equally brilliant colours (while 
both sexes are rarely armed with equally developed 
offensive and defensive weapons when not required for 
individual safety), that the normal action of ‘sexual 
selection”? is to develop colour and beauty in both 
sexes, by the preservation and multiplication of all 
varieties of colour in either sex which are pleasing 
