The Malay archipelago : the land of the orang-utan ... - Wallace Online

102 THE MALAY ARCHIPELAGO. [chap.varies much, but it is always some ashy brown or reddisli colour,which matches with those of dead leaves. The habit of thespecies is always to rest on a twig and among dead or dryleaves, and in this position with the wings closely pressed together,their outline is exactly that of a moderately-sized leaf,slightly curved or shrivelled. The tail of the hind -^dngs formsa perfect stalk, and touches the stick while the insect is supportedby the middle pair of legs, which are not noticed amongthe twigs and fibres that surround it. The head and antennfeare drawn back between the A^-ings so as to be quite concealed,and there is a little notch hollowed out at the very base of thewings, which allows the head to be retracted sufficiently. Allthese varied details combine to produce a disguise that is socomplete and marvellous as to astonish every one who observesit ; and tlie habits of the insects are such as to utilize all thesepeculiarities, and render them available in such a manner as toremove all doubt of the purpose of this singular case of mimicry,which is undoubtedly a protection to the insect. Its strong andswift flight is sufficient to save it from its enemies when on thewang, but if it were eqiaally conspicuous when at rest it couldnot long escape extinction, owing to the attacks of the insectivorousbirds and reptiles that abound in the tropical forests.A very closely allied species, Kallima inachis, inhabits India,where it is very common, and specimens are sent in everycollection from the Himalayas. On examining a number ofthese, it will be seen that no two are alike, but all the variationscorrespond to those of dead leaves. Evexy tint of yellow, ash,brown, and red is found here, and in many specimens thereoccur patches and spots formed of small black dots, so closelyresembling the way in which minute fungi grow on leaves thatit is almost impossible at first not to belieA'e that fungi havegrown on the butterflies themselves !If such an extraordinary adaptation as this stood alone, itwould be very difficult to ofier any explanation of it ; butalthough it is perhaps the most perfect case of protective imitationknown, there are hundreds of similar resemblances innature, and from these it is possible to deduce a general theoryof the manner in which they have been slowly brought about.The principle of variation and that of " natural selection," orsurvival of the fittest, as elaborated by Mr. Darwin in hiscelebrated Orit/in of Sijecics, otters the foundation for such atheory ; and I have myself endeavoured to apply it to all thechief cases of imitation in an article published in the WesfminsterReview for 1867, entitled "Mimicry, and other Protective Eesemblancesamong Animals," to which any reader is referredwho wishes to know more about this subject.^In Sumatra, monkeys are very abundant, and at Lobo Ramanthey used to frequent the trees which overhang the guard-house,1 This article forms tlic third chapter of my Natural Selection and Tropical Nature.