340 TROPICAL NATURE v 
and emotions may not be another and perhaps more important 
use which they subserve in the great system of the universe ? 
We now propose to lay before our readers a general account 
of the more recent discoveries on this interesting subject ; and 
in doing so it will be necessary first tu give an outline of the 
more important facts as to the colours of organised beings ; 
then to point out the cases in which it has been shown that 
colour is of use ; and lastly, to endeavour to throw some light 
on its nature and on the general laws of its development. 
Among naturalists, colour was long thought to be of little 
import, and to be quite untrustworthy as a specific character. 
The numerous cases of variability of colour led to this view. 
The occurrence of white blackbirds, white peacocks, and black 
leopards, of white blue-bells, and of white, blue, or pink milk- 
worts, led to the belief that colour was essentially unstable, 
that it could therefore be of little or no importance, and 
belonged to quite a different class of characters from form or 
structure. But it now begins to be perceived that these 
cases, though tolerably numerous, are, after all, exceptional ; 
and that colour, as a rule, is a constant character. The great 
majority of the species, both of animals and plants, are each 
distinguished by peculiar tints which vary very little, while 
the minutest markings are often constant in thousands or 
millions of individuals. All our field buttercups are invari- 
ably yellow, and our poppies red, while many of our butter- 
flies and birds resemble each other in every spot and streak of 
colour through thousands of individuals. We also find that 
colour is constant in whole genera and other groups of species. 
The Genistas are all yellow, the Erythrinas all red; many 
genera of Carabide are entirely black ; whole families of birds 
—as the Dendrocolaptidee—are brown; while among butter- 
flies the numerous species of Lycena are all more or less blue, 
those of Pontia white, and those of Callidryas yellow. An ex- 
tensive survey of the organic world thus leads us to the conclu- 
sion that colour is by no means so unimportant or inconstant 
a character as at first sight it appears to be; and the more we 
examine it the more convinced we shall become that it must 
serve some purpose in nature, and that, besides charming us 
by its diversity and beauty, it must be well worthy of our 
attentive study, and have many secrets to unfold to us. 
