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Page:Popular Science Monthly Volume 42.djvu/201

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COLORATION OF LAND SNAILS.

PROTECTIVE DEVICES AND COLORATION OF LAND SNAILS.
By HENRY A. PILSBRY,

CONSERVATOR, DEPARTMENT OF MOLLUSCA, ACADEMY OF NATURAL SCIENCES OF PHILADELPHIA.

THIRTY years ago, when Bates wrote his modest observations upon the protective mimicry of the butterflies of the Amazons, few naturalists could have foreseen the vital and far-reaching influence those now classic pages would have upon the future of biology. But the new doctrine, taken up by Darwin, Wallace, and others, and illustrated by hundreds of examples among insects, birds, and mammals, has already taken its place among the established canons of zoölogy.

The general principles of the subject of mimicry are now familiar to the laity as well as to scientists; but much still remains for observation at our very doors, to supplement the known facts, and to extend the underlying principles of mimicry and protective resemblance to the less-known groups of animals, among which are the land mollusks.

We have been made familiar with many cases of what may be called true mimicry, occurring among the insects; such as the conspicuous resemblance some moths, which are of course both defenseless and edible, bear to wasps and other stinging insects; and the instances of edible butterflies mimicking in their colors nauseous species are also well known. A more striking case of this phase of mimicry has quite recently been noticed in tropical America. In the forests of this region, leaf-cutting ants live in countless numbers. They strip whole trees of their foliage, carrying the leaves in fragments to their formicaries. Now, among these ants have been found insects belonging to an entirely different order, which mimicked the ant and its leafy burden! The back of the mimicking insect is green, and pinched up into a flat, thin plate, quite the counterpart of the leaf-fragment carried by the ant.[1]

A much more simple case is represented by the dead-leaf butterfly of Java, which, when it alights upon a bush, presents so close a resemblance to a dead leaf that even so experienced a naturalist as Wallace was long deceived by it. This resemblance of an animal to its surroundings may be called "protective resemblance," rather than mimicry.

Instances such as these might be multiplied indefinitely, were we to confine ourselves to the insect world. The great variety of


  1. See the article by Edward D. Poulton on this insect, Proceedings of the Zoölogical Society of London, 1891.