at 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 innumerable 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 protective, as in the case of arctic animals and aquatic birds,
it appears freely enough; while we know that white varieties of many
species occur occasionally in the wild state, and that, under
domestication, white or parti-coloured breeds are freely produced. Now
in all the islands in which exceptionally white-marked birds and
butterflies have been observed, we find two features which would tend to
render the conspicuous 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 review of the whole subject, then, we 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; while, on the other hand, the two great
principles of the need of concealment from enemies or from their prey,
and of recognition by their own kind, are so wide-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, we are acquainted
with other modes of coloration which have a different origin. These
chiefly appertain to the very singular class of warning 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
will be required by the subject of sexual differentiation of colour and
ornament, as to the origin and meaning of which I have arrived at
different conclusions from Mr. Darwin. These various forms of coloration
having been discussed and illustrated, we s