4A THEORY OF BIRDS’ NESTS. 263 
require the aid of insects to fertilize them, and main- 
tain 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 fertilized by the wind, and do not need 
the aid of insects, rarely or never have gaily-coloured 
flowers. 7 
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 
I have given of the facts adduced in this essay, I 
would again respectfully urge that they must grapple 
with the whole of the facts, not one or two of them 
only. It will be admitted that, on the theory of 
evolution and natural selection, a wide range of facts 
with regard to colour in nature havé been co-ordi- 
nated and explained. Until at least an equally wide 
range of facts can be shown to be in harmony with 
any other theory, we can hardly be expected to aban- 
‘don that which has already done such good service, 
and which has led to the discovery of so many in- 
teresting and unexpected harmonies among the most 
common (but hitherto most neglected and least un- 
derstood), of the phenomena presented by organised 
beings. 
