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Show 290 DARWINISM OIIAP. as the animal grows older; then the s~ripes expand, ::tnd at last, meeting together, the adult amm::tl becomes. of a uniform dark brown colour. So many of the specws of deer are spotted when young, that D::trwi:l concludes the ::tncestral form, from which all deer are denved, must have been spotted. Pigs and t::tpirs are banded or sRotted w?CJ~ young ; an imported young specimen . of . Tapn·us Bamh was covered with white spots in long1tudm::tl rows, here a.nd there forming short stripes.1 Even tho horse, which Darwin supposes to bo descended from a striped ::tnim::tl, is often spotted, as in dappled horses; and grca,t numbers show a tendency to spottincss, especially on tho h::tunches. Ocelli may also be developed from spots, or from bars, as pointed out by Mr. D::trwin. Spots arc an ordinary form of marking in disease, and these spots sometimes run together, forming blotches. There is evidence that colour marking. arc in some way dependent on nerve distribution. In the di sease known as frontal herpes, an eruption occurs which corresponds exactly to tho distribution of the ophthalmic division of tho fifth cranial nerve, m::tpping out all its little branches even to the one which goes to the tip of the nose. In a Hindoo suffering from herpes tho pigment was destroyed in tho arm along the course of the ulnar nerve, with its branches along both sides of one finger and the half of another. In the leg the sciatic and scaphcnous nerves were partly mapped ont,, giving to the patient tho appearance of an anatomieal diagram.2 These facts are very interesting, because they help Lo explain the general dependence of marking on structure which has been already pointed out. For, as the nerves everywhere follow the muscles, and these are attached to the va,rious hones, we see how it happens, that the tracts in which di. tincL developments of colour appear, should so often be marked onL by the chief divisions of tho bony structure in vertebrates, :uul by the segments in the annulosa. There is, however, another correspondence of even greater interest and importanee. Brilliant colours usually appear just in proportion to the 1 See coloured Fig. in Proc. Zool. Soc., 1871, p. 626. 2 A. Tylor's Colomtion, p. 40 ; and Photograph in Hutchinson's Ill ustrations of Clinical Surge1·y, qLwted by Tylor. x COLOURS AND ORNAMENTS CHARACTERISTIC OF SEX 291 development of tegumentary appendages. Among birds tho most brillia,nt colours are possessed by those which have developed frills, crests, and elongated tails like the hummingbirds; immense tail-coverts lilw the peacock; enormously expanded wing-feathers, as in the argus-pheas::tnt; or magnificent plumes from tho region of tho coracoids in many of the birds of paradi. c. It is to be noted, a.lso, that all these accessory plumes spring from parts of the body which, in other species, arc di. tinguishccl by patches of colour; so that we ma.y probably impute tho development of colour and of accessory pluma.gc to the same fundamental ca.use. Among insects, the most brilliant and varied coloration occurs in tho butterflies and moths, gronps in which the wingmembranes have received their greatest expansion, and whoso specialisation has been carried furthest in the marvellous scaly covering which is the seat of tho colour. It is suggestive, that the only other group in which functional wings arc much coloured is that of the dragonflies, whore the membrane is exceedingly expanded. In like mmmer, the colours of beetles, though greatly inferior to those of tho lcpicloptcra, occur in a group in which tho anterior pair of wings has been thickened and modified in order to protect the vita.l parts, and in which these wing-covers ( clytra), in the cour·sc of development in tho different groups, must have undergone great changes, and have been the seat of very active growth. The 01·igin of Accesso1·y Phtmes. Mr. Darwin supposes, that those have in almost every case been developed by the preference of female birds for such males as possessed them in a higher degree than others ; hnt this theory does not account for the fact that these plumes nsn:tlly ·appear in a few definite parts of tho body. \V c require some cause to initiate the development in one part rather than in another. Now, the view that colour has arisen over surfaces whore muscular and nervous development is considerable, and tho fact that it appears especially upon the accessory or highly developed plumes, loads us toinqnircwhcther the same cause has not primarily determined the development of those plumes. The immense tnft of golden plumage in the best known birds of paradise (Paradisea apoda and P. minor) |
