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Show 264 DARWINISM CHAP. have a patch of bare black skin round the eyes, and a ruff of curious pale recurved feathers on the nape, whence their name of Friar-birds, the ruff being suppo. ed to resemble the cowl of a friar. These peculiarities are imitated in the orioles by patches of feathers of corresponding colours ; w bile the different tints of the two species in each island are exactly the arne. Thus in Bouru both are earthy brown; in Ceram they are both washed with yellow ochre ; in Timor the under nrface is pale and the throat nearly white, and Mr. H. 0. Forbes has recently discovered another pair in the island of Timor Laut. The close resemblance of these several pairs of birds, of widely different families, is quite comparable with that of many of the insects already described. It is so close that the preserved specimens have even deceived naturalists ; for, in the great French work, Voyage de l'Ast?·olabe, the oriole of Bourn is actually described and figured as a honey-sucker ; and Mr. Forbes tells us that, when his birds were submitted to Dr. Sclater for description, the oriole and the honey-sucker were, previous to close examination, considered to be the same species. Objections to the Theory of Jl{imicry. To set forth adequately the varied and surprising fact. of mimicry would need a large and copiou ly illustrated volume; and no more interesting subject could be taken up by a, naturalist who has access to our great collections and can devote the necessary time to search out the many example · of mimicry that lie hidden in our museums. The brief sketch of the subject that has been here given will, however, serve to indicate its nature, and to show the weakness of the obj ections that were at first made to it. It was urged that the action of "like conditions," with "accidental resemblances" and "reversion to ancestral type ,"would account for the fcwts. lf, however, we consider the actual phenomena as here set for th, and the very constant conditions ·under which they occur, we shall see how utterly inadequate are the. e cau. ·es, either singly or combined. These constant conditions are- 1. That the imitative species occur in the same area u,n(l occupy the very same station as the imitated. 2. That the imitators are always the more defenceless. IX WARNING COLORATION AND MIMICRY 265 3. That the imitators are always less numerous m mdividual . 4. That the imitators differ from the bulk of their allies. 5. T~a~ the imitation, however minute, is e~J.:tenutl and v~stble only, never extending to internal character or to such as do not affect the external appearance. . !hese five characteri_stic features of mimicry show us that It IS really an exceptiOnal form of protective re. emblance. Differe~t speci~s in the same group of organisms may obtain protec~10n m. different way : some by a general re emblance to. tbmr environment; some hy more exactly imitating the obJects th~t su~Tound them-bark, or leaf, or flower; while othe:s agm~t gam an equal protection by re embling some speciCs whiCh, from whatever can. e, is almo. t as free from attack as if. it w.ere a leaf or a flower. This immunity may depend on Its bemg uneatable, or dancrerous or merely . trono· . and it ~s t~e res?mblance to such creatur~es for the purpo0 ~ of shanng m their safety that constitutes mimicry. Concluding Rema1·lcs on !Va1·ning Colo'ttrs and 1vlimicry. . Colours whic~ have b_een ~c.q.uired for the purpose of . ervmg as a warn~ng of mechb1hty, or of the po ses ion of dangerous offensive weapons, are probably more num l'Ous than have been hitherto supposed; and, if so, we hall be able to explain a considerable amount of colour in nature for which no use has hitherto been conjectured. The brilliant and v~ried colours of sea-anemones and of many coral a,nimnJs w1ll probably come under this head, since we know that many of. them possess the power of ejecting stinging threads from variOus parts of ~heir bodies which render them quite uneatable to most ammals. Mr. Gosse describes how on putting an Anthea into a tank containin()' a half- o·1:own b.ullhead (Cottus bubalis) which had not be~n fed for 0 ome time, the fish opened his mouth and sucked in the mor el b.ut instantly shot it out again. He then seized it a secoml time, and after rolling it about in his mouth for a moment ~hot it out again, and then darted away to hide him elf m a hole. Some tropical fishes, however, of the genera Tetrodon, Pseudoscarus, Astracion, and a few others, seem |