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Show 230 DARWINISM OIIAJ>. So many cases arc adduced from so many different islands, both in the eastern aud 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 wehaveone of the almost innumcr 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. vVhencvcr it becomes pro tective, as in the case of arctic animals ~~nd aquatic bird s, it appears freely enough; while we know tha,t white varieties of many species occur occasiom1lly in the wHd state, an<l that, under domestication, white or parti-colourccl breeds arc 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 COIL~ spicuous white markings less injurious-a luxuriant tropil'al vegetation, and a decided scarcity of rapacious mammals ttll<l birds. White colours, therefore, would not bo climirw tc<l by natural selection; but variations in this direction wonl\l bear their part in producing tho 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, wo must conclude that there is no evidence of the individuaJ or prevalent colours of organisms b?ing dircctly.determincd by the amount of light,, or heat, or mmsturc, to whiCh they are exposed ; while, OIL the other hand, the two great principles of the nco l of concealment from enemies or from their prey, and of recognition hy their own kind, arc so wide-reaching in their application that th<'y appear at first sight to cover almost tho whole rrrollnd of animal coloration. Bnt, although they arc indeed w~ n <lerfttlly general and hn.vc as yet been very imperfectly . tndicd, 1re arc acquainted with other modes of coloration which h,~,·e a different origin. These chiefly appertain to the very singnLu· class of warning colours, from which arise the yet more extraordinary phenomena of mimicry; and they open up so curions ~~ field of inquiry and present so many interesting problems, that a chapter must he devoted to them. Y ct another chapter will vnr ORIGIN AND USES OF COLOUR IN ANIMAL~ 231 be required by the subject of sexual differentiation of colour and ornament, as to the origin and meaning of which I havo arrived at different conclusions from Mr. Darwin. These various forms of coloration having been discussed and illustrated, wo shall be in a position to attempt a brief sketch of the fundamental laws whiclt have determined the gcncra1 coloration of the animal world. |
