vi A THEORY OF BIRDS’ NESTS 139 
ence of the species. Colour has hitherto been too often looked 
upon as something adventitious and superficial, something 
given to an animal not to be useful to itself, but solely to 
gratify man or even superior beings—to add to the beauty 
and ideal harmony of nature. If this were the case, then, it 
is evident that the colours of organised beings would be an 
exception to most other natural phenomena. They would not 
be the product of general laws, or determined by ever-chang- 
ing external conditions ; and we must give up all inquiry into 
their origin and causes, since (by the hypothesis) they are 
dependent on a Will whose motives must ever be unknown to 
us. But, strange to say, no sooner do we begin to examine 
and classify the colours of natural objects, than we find that 
they are intimately related to a variety of other phenomena, 
and are, like them, strictly subordinated to general laws. I 
have here attempted to elucidate some of these laws in the 
case of birds, and have shown how the mode of nidification 
has affected the colouring of the female sex in this group. I 
have before shown to how great an extent, and in how many 
ways, the need of protection has determined the colours of 
insects, and of some groups of reptiles and mammalia, and I 
would now call particular attention to the fact that the gay 
tints of flowers, so long supposed to be a convincing proof that 
colour has been bestowed for other purposes than the good of 
its possessor, have been shown by Mr. Darwin to follow the 
same great law of utility. Flowers do not often need pro- 
tection, but very often require the aid of insects to fertilise 
them, and maintain their reproductive powers in the greatest 
vigour. Their gay colours attract insects, as do also their 
sweet odours and honeyed secretions; and that this is the 
main function of colour in flowers is shown by the striking 
fact that those flowers which can be perfectly fertilised by 
the wind, and do not need the aid of insects, rarely or never 
have gaily-colowred flowers. 
This wide extension of the general principle of utility to 
the colours of such varied groups, both in the animal and 
vegetable kingdoms, compels us to acknowledge that the 
“reign of law” has been fairly traced into this stronghold of 
the advocates of special creation. And to those who oppose 
the explanation now given of the various facts bearing upon 
