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Show 226 DARWINISM OllAl'. on the head or neck, often not interfering with the generally protective character of their plumage. Such arc the bright patches of blue, red, or yello·w, by which the usually green Eastern barbets arc distinguished; and similar bright patches of colour characterise the separate species of small green fruit-doves. To this necessity for specialisation in colom, hy which each bird may easily recognise its kind, is probably dne that marvellous variety in the peculiar beauties of some gronps of birds. The Duke of Argyll, speaking of the bumming birds, made the objection that "A crest of topaz is 110 better in the struggle for existence than a crest of sapphi r·c. A frill ending in spangles of the emerald is no better in the battle of life than a frill ending in spangles of the rn by. A tail is not affected for the purposes of flight, whether its marginal or its central feathers arc docornted with whi te';" and he goes on to urge that mere hcanty and variety for their own sake are the only cause. of these difl'cron cos. H11 t, on the principles here suggested, tho divergence itself is mdnl, and must have boon produced pa1·i pa.·su with the strnctnral differences on which the differentiation of species depends; and thus we have explained the curious fact that promirH'IIt differences of colour often distinguish species otherwise , cry closely allied to each other. Among insects, the principle of distinctive coloration for recognition has probably been at work in the proclnction of the wonderful diversity of colour and markirw we find CYcrywhere, more especially among the butterflies and moths · and here its chi_ef !u.nction may have boon to secure the p~iring together of md1v1duals of the same species. In some of tho moths this has been secured by a peculiar odour, whi<'h attracts the males to tho females from a eli. tanco; but th n' i:-; no evidence that this is universal or even general and amon" butterflies, especially, the characteristic colom a;1d markin(~ aided by size and form, afford tho most proha blo moan~ ~f recognition. That this is so is shown by the fact that "the common white butterfly often flies down to a hit of paper on the ground, no doubt mistaking it for one of its own specicil;" while, according to Mr. Collingwood, in the MnJay Archipelago, "a dead butterfly pinned upon a conspicuous twio· will often . 0 arrest an msect of the same species in its headlong flight, ami Vlri ORICUN AND USES OF COLOUR IN ANIMALS 227 bring it clown within easy reach of the net, especially if it be of tho opposite scx." 1 In a great nnmhcr of insects, no doubt, form, motions, stri(lulating sound., or peculiar odours, serve to distinguish allied species from each other, and this must be especially the ca. c with nocturnal in. ccts, or with those whose colours arc nearly uniform and arc determined by the need of protection; bnt by far the larger number of day-flying and activo insect. exhibit varieties of colour and marking, forming tho most obvious distinction between allied species, and which have, therefore, in all probability been acquired in the procc. s of differentiation for the purpose of chocking the intercrossing of closely nJli o<.l forms. 2 Whether this principle cxtondil to n.ny of the less highly organised a11imnJs is donhtfnl, though it mc.ty perha.p · have affected the higher mollu. C<t. But in marine animals it seems probable th:tt tho colours, however hcn.utiful, varied, and brilliant they may often he, are in most cases protective, assimilating them to the va,rions hright-colomocl Reawoeds, or to some other animals which it is ad vantagoous for them to imitatc.3 Summa1·y of the Preceding Exposition. Before proceeding to discu s some of tho more recondite phenomena of animal coloration, it will be well to consider for a moment tho extent of tho ground we have already covered. Protective coloration, in some of its varied forms, has not improbably modified the appearance of one-half of the n.nimals living on the globe. Tho white of arctic animals, the yellowish tints of the desert forms, the dusky hues of crepuscular and nocturnal species, tho transparent or bluish tints of oceanic creatures, represent a vast host in themselves; hut we have n.n equally numerous body whoso tints ::tro adapted to tropical foliage, to the bark of trees, or to tho soil 1 Quoted by Darwiu in Descent of .. Man, p. 317. 2 In the !lme1·ican Natumlist of March 18 8, Mr. J. E. Todd has an article on" Directive 'oloratioa in Animals," in whi t:h he recognise!> many of the cases here referred to, :wd suggests a few others, though I think he includes many fonns of coloration- ns "paleness of belly and iuner side of legs "- which do not belong to this class. 3 For numerous examples of this protective colouring of marine animals see l\'foseley's Voya,qe of the Challeuger, and Dr. E. S. Morse in Proc. of Bast. Soc. of Nett. lfist., vol. xiv. 1871. |