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Show 244 DARWINISM CHAP. the former and reject the latter. The Pioridm would, however, usually be less numerous, because their hrvm arc often protectively coloured and therefore edible, while tho larvre of the Heliconidre arc :Ldorncd with warning colours, spines, or tubercles, and arc uneatable. It seems probable that tlH' larvre and pupm of the Hcliconidre were the first to acgnirt' the protective eli tn tefnlncs , both because in this stag<' th ey n.rc more defcncclc s a.Jl(l more liable to fatal injury, a,tl(l ai Ko lJecausc wo now find many instances in which the larva: arc distasteful while tho perfect insects arc ea.bLblc, bnt I lJclic\ 0 none in which the reverse is the case. The larvre of the Picridre are now beginning to acquire offensive jui ceR, hnt have not yet obtained the corresponding con. picnon. colonr::; · while the perfect insects remain eatable, cxc:ept pcrktps i 1; some Eastern groups, the under sides of whose wingK are brilliantly colomccl although this is the part which is exposed when at re ·t. It is clear that if a large m~jority of tho larvre of Lepidoptera, as well as the perfect insects, acquired th so cli Kt:tKteful propertic , so as seriously to diminish tho footl supply of insectivorous and nestling birds, those latter would be fo;·<'cd by necessity to acquire corresponding tastes, and to cat with plea. ure what some of them now cat only under prcsRurc of hnnaer; and variation and natural selection would . oon llJ'in~r about this ch:Lnge. 0 Many writers have denied the possibility of . uch worHlcrfnl resemblances being produced by the accumubtion of for tuitous vn.riations, but if the reader will call to mi ncl the lm· o·c amon11t of variability that has been shown to exist in all ~rgn uisllls, the exceptional power of rapid increase pos essed by in ccts, and the tremendous strugcrlc for existence alwa.ys o·oinu on the difficulty will vanish, especially when we rc~1enili •r 'that nature has the same fundamental groundwork to act upon in the two groups, general similarity of forms, wings of .. imil:tr texture and outline, and probably some original similarity of colour and marking. Yet there is evidently considern hln difficulty in the process, or with these grca.t resources at her command nature would have produced more of the. c mimicking forms than she has done. One rca on of this defi ciency probably is, that the imitators, being always fewer in numher, have IX WARNING COLORATION AND MIMICRY 245 not been able to keep pace with the variations of the much more numerous imitated form ; another reason may be the ever-increasing acuteness of the enemies, which have again a.ncl nga.in detected the imposture and exterminated the feeble race before it has had time to become further modified. The result of this growing acuteness of enemies has been, that those mimics that now survive exhibit, as Mr. Bates well remarks, "a palpably intentional likeness that is perfectly staggering," and also "that those features of the portrait are most attended to by nature which produce the most effective deception when the insects arc seen in nature." No one, in fact, ca.n understand the perfection of the imitation who has uot seen these species in their native wilds. So complete is it in general effect that in almost every box of butterflies, brought from tropical America by amateurs, are to be found some species of the mimicking Picridre, Erycinidro, or moths, and the mimicked Heliconidre, placed together under the imprc sion that they are the same species. Yet more extraonlinary, it sometimes deceives the very insects themselves. Mr. Trimen states that the male Danais chrysippus is sometimes deceived by the female Diaclema bolina which mimics that species. Dr. Fritz MUller, writing from Brazil to Professor Melclola, says, " One of the most interesting of our mimicking butterflies is Leptalis melite. The female alone of this species imitates one of our common white Pieridre, which ·he copies so well that even her own male is often deceived; for I have repeatedly seen the malo pursuing the mimicked species, till, after closely approaching and becoming aware of his error, he suddenly returncd." 1 This is evidently not a case of true mimicry, since the species imitated is not protected; but it may be that the less abundant Leptalis is able to mingle with the female Pieridre and thus obtain partial immunity from attack Mr. Kirby of the insect department of the British Museum informs me that there aro several species of South American Pieridre which the female Leptalis melitc very nearly resembles. The case, however, is interesting as showing that the butterflies arc themselves deceived by a resemblance which is not so great as that of some mimicking species. 1 R. Meldola in Ann. and .Mag. of Nat. llist., Feb. 1878, p. 158. |