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Show 256 DARWINISM CHAP. closely allied forms-those that require minute examination to discriminate them as distinct species-are most gencrnJ]y found in separate areas, and are what are termed representative forms. The extension we have now given to the theory of mimicry i important, since it enables us to expl~in a much wi ~l er rano-e of colour phenomena than those whiCh were first Inl put~ d to mimicry. It is in the richest butterfly rcfrion in the world-the Amazon valley-that we find the most <thundant evidence of the three distinct sets of facts, all depend in ,,. o r1 the same general principle. The form of mimicry first elucidated by Mr. Bates is characterised by the presence in each locality of certain butterflies, or other insects, themscl ves edible and belonging to edible groups, which derived protection from having acquired a deceptive re. emblance to some of the inedible butterflies in the same localities, which latter were believed to be wholly free from the attacks of insectivorous birds. Then came the extension of the principle, by Dr. F. Muller, to the case of species of distinct genera of the inedible butterflies resembling each other quite as closely as in the former cases, and like them always found in the same localities. They derive mutual benefi t from becoming, in appeara,nce, one specie. , from which a Cl'l'tain toll is taken annually to teach the young insectivorous l1inls that they are uneatable. Even when the two or more species are approximately equal in numbers, they each derive a considerable benefit from thus combining their forces ; hut when one of the species is scarce or verging on extinctio11, the benefit becomes exceedingly great, being, in fact, exactly apportioned to the need of the species. The third extension of the same principle explains the grouping of allied species of the same genera of inedible butterflies into sets, each having a distinct type of coloration, and each consisting of a number of species which can hardly be distinguished on the wing. This must be useful exactly in the same way as in the last case, since it divides the inevitable toll to insectivorous birds and oth er aniwa,ls among a number of species. It also explains the fact of the great similarity of many species of inedible insects in ~h e same locality-a similarity which does not obtain to anythmg IX WARNING COLORATION AND MIMICRY 257 like the same extent among the edible species. The explanation of the various phenomena of resemblance and mimicry, presented by the distasteful butterflies, may now be considered tolerably complete. llf.imicry in other 01·de1·s of Insects. A very brief sketch of these phenomena will be given, chiefly to show that the same principle prevails throughout nature, and that, wherever a rather extensive group is protected, either by distastefulness or offensive weapons, there are usually some species of edible and inoffensive groups that gain protection by imitating them. It has been already stated that the Telephoridre, Lampyridre, and other familic. of . oft-winged beetles, arc distasteful; and as they abound in all parts of the world, and especially in the tropics, it is not surprising that insects of many other groups should imitate them. This is especial1y the case with the longicorn beetles, which arc much persecuted by insectivorous birds; and every·where in tropical regions some of these are to be found so completely disguisetl as to be mistaken for species of the protected groups. Numbers of these imitations have been already recorded by Mr. Bates and myself, but I will here refer to a few others. In the recently published volumes on the Longicorn and Malacoclerm beetles of Central America 1 there are numbers of beautifully coloured figures of the new species; and on looking over them we are struck by the cmious resemblance of some of the Longicorns to species of the Malacoderm group. In some cases we discover perfect mimics, and on turning to the descriptions we always find these pairs to come from the same locality. Thus the Otheostethus melanurus, one of the Prionidre, imitates the malacoderm, Lucidota discolor, in form, peculiar coloration, and size, and both are found at Chontales in Nicaragua, the species mimicked having, however, as is usual, a wider range. The curious and very rare little longicorn, Tethlimmena aliena, quite unlike its nearest allies in the same country, is an exact copy on a somewhat smaller scale of a malacoderm, Lygistopterus amabilis, both I Godman and Salvin's Biologict Centrali-Americana, Insecta, Coleoptera, vol. iii. part ii., and vol. v. |