230 
DARWINISM 
CHAP. 
So many cases are adduced from so many different islands, both 
in the eastern and western hemisphere, that it is impossible 
to doubt the existence of some common cause; and it seems 
probable to me now, after a fuller consideration of the whole 
subject of colour, that here too we have one of the almost innumer¬ 
able results of the principle of protective coloration. White is, 
as a rule, an uncommon colour in animals, but probably only 
because it is so conspicuous. Whenever it becomes pro¬ 
tective, as in the case of arctic animals and aquatic birds, it 
appears freely enough ; while Ave know that Avhite varieties 
of many species occur occasionally in the wild state, and 
that, under domestication, white or parti-coloured breeds are 
freely produced. Noav in all the islands in which exception¬ 
ally white-marked birds and butterflies have been observed, 
Ave find tAvo features Avliich would tend to render the con¬ 
spicuous white markings less injurious—a luxuriant tropical 
vegetation, and a decided scarcity of rapacious mammals and 
birds. White colours, therefore, would not be eliminated 
by natural selection; but variations in this direction would 
bear their part in producing the recognition marks which 
are everywhere essential, and which, in these islands, need 
not be so small or so inconspicuous as elsewhere. 
Concluding Remarks. 
On a revieAv of the whole subject, then, Ave must conclude 
that there is no evidence of the individual or prevalent colours 
of organisms being directly determined by the amount of light, 
or heat, or moisture, to which they are exposed ; Avliile, on the 
other hand, the tAvo great principles of the need of concealment 
from enemies or from their prey, and of recognition by their 
own kind, are so Avide-reaching in their application that they 
appear at first sight to cover almost the whole ground of 
animal coloration. But, although they are indeed wonderfully 
general and have as yet been very imperfectly studied, avc are 
acquainted Avith other modes of coloration which have a 
different origin. These chiefly appertain to the very singular class 
of Avarning colours, from which arise the yet more extraordinary 
phenomena of mimicry ; and they open up so curious a field 
of inquiry and present so many interesting problems, that a 
chapter must be devoted to them. Yet another chapter Avill 
