Page:Popular Science Monthly Volume 42.djvu/203

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color of the animal corresponds with the prevailing color of the environment, and thus it escapes the notice of its enemies.

A more complex state of affairs exists in those animals which make use of external objects for their own concealment. A case in point is the hairy snail (Helix hirsuta), a species commonly found throughout the Northern States, living around decaying logs in the forests. These little fellows have a clothing of short hair all over the shell, and this hair holds so much of the soil that they look more like small pellets of earth than like snail-shells. The disguise is effective enough to deceive more acute shell-collectors than the birds.

PSM V42 D203 Helix hirsuta showing hairy cuticle.jpg
Fig. 1.—Helix hirsuta. Showing hairy cuticle.

An altogether similar attempt at deception is practiced by a marine mollusk, the so-called "carrier." This gastropod has a broad spiral shell, to the upper surface of which it cements shells or pebbles, until finally it appears to be nothing more than a heap of shell-fragments, not distinguishable from any other irregularity of the sea-bottom. Another instance may be mentioned, as it illustrates the extension of this general principle to widely different groups of animals. The sea-urchins of our coasts have often been observed to cover themselves completely with small stones, so that nothing can be seen but a heap of pebbles.

Coming back to our hairy Helix, we may perhaps credit its hirsute coat with an additional function besides mere dirt-gathering. Poulton has observed that some insectivorous animals have an excessive repugnance for hairy insect larvæ, even when they

PSM V42 D203 Three toothed snail and carolus labyrinthus.jpg
Fig. 2.—Three-toothed Snail, Helix tridentata. Illustrating the simplest form of obstructing teeth. Fig. 3.—Caracolus labyrintihs—a South American forest snail. Showing extreme development of lip-teeth.

are not otherwise repulsive. The marmoset, for instance, can not be induced to touch any hairy larva. It is not improbable that small mammals, such as moles and field-mice, find the hairy covering of Helix hirsuta disagreeable, although we know that they eat other snails.

An old collector, who had spent most of his life within the