[Illustration: Fig. 19.--A locust (_Cycloptera speculata_) which closely resembles a leaf. (From an exhibit in the British Natural History Museum.)] Perhaps one of the most striking instances of special protective resemblance is that of the Malayan leaf-butterfly (_Kallima paralecta_). So completely, when the wings are closed, does this insect resemble a leaf that it requires a sharp eye to distinguish it. These butterflies have, moreover, the habit of alighting very suddenly. As a recent observer (Mr. S. B. T. Skertchly) remarks, they "fly rapidly along, as if late for an appointment, suddenly pitch, close their wings, and become leaves. It is generally done so rapidly that the insect seems to vanish."[AB] Instances might be multiplied indefinitely. Mr. Guppy thus describes a species of crab in the Solomon Islands: "The light purple colour of its carapace corresponds with the hue of the coral at the base of the branches, where it lives; whilst the light red colour of the big claws, as they are held up in their usual attitude, similarly imitates the colour of the branches. To make the guise more complete, both carapace and claws possess rude hexagonal markings which correspond exactly in size and appearance with the polyp-cells of the coral."[AC] When the special protective resemblance is not to an inanimate object, but to another organism, it is termed mimicry. It arises in the following way:-- Many forms, especially among the invertebrates, escape elimination by enemies through the development of offensive weapons (stings of wasps and bees), a bitter taste (the Heliconidæ among butterflies), or a hard external covering (the weevils among beetles). The animals which prey upon these forms learn to avoid these dangerous, nasty, or indigestible creatures; and the avoidance is often instinctive. It thus becomes an advantage to other forms, not thus protected, to resemble the animals that have these characteristics. Such resemblance is termed mimicry, concerning which it must be remembered that the mimicry is unconscious, and is reached by the elimination of those forms which do not possess this resemblance. Thus the _Leptalis_, a perfectly sweet insect, closely resembles the _Methona_, a butterfly producing an ill-smelling yellow fluid. The quite harmless _Clytus arietis_, a beetle, resembles, not only in general appearance, but in its fussy walk, a wasp. The soft-skinned _Doliops_, a longicorn, resembles the strongly encased _Pachyrhyncus orbifex_, a weevil. The not uncommon fly _Eristalis tenax_ (Fig. 20), is not unlike a bee, and buzzes in an unpleasantly suggestive manner.[AD]