Variation and Natural Selection. 87 



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." * 



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 offen- 

 sive weapons (stings of wasps and bees), a bitter taste (the 

 Heliconidae 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 in- 

 stinctive. 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. f 



* Nature, vol. xxxv. p. 77. 



t Many other instances might be added. The hornet clear-wing moth 

 (Sphecia apiformis) mimics the hornet or wasp; the narrow-bordered bee- 

 hawk moth (Sesia bombyliformis) mimics a bumble-bee. These insects may- 

 be seen in the lepidoptera drawers in the Natural History Museum. But 

 perhaps the most wonderful instance of insect-mimicry is that observed 



