some animals—such as the leaf insects and walking-stick insects—to the extent of close and actual mimicry, our surprise is increased.
Or, lastly, when we find, as in the latest phase of modern warfare, that the concealed torpedo is used as a subtile and powerful means for effecting the destruction of whole fleets, the fact cannot but call to mind the electrical apparatus of some fishes—and notably that of the torpedo or electric ray—which exists as a natural means of defense, the powers of which, few, if any, of their less favored neighbors care to test or provoke.
While the consideration of the more prominent and typical means of defense in animals may very reasonably occupy our brief attention, a few words on the subject of mimicry in the animal series may also prove interesting, more especially as this form of protection, through imitation of their surroundings, forms a simple yet effective means of defense to many organisms. We have already referred to the readily-perceived and very general correspondence in color seen throughout the animal world between animals and their abodes; and of the more general aspects of this condition nothing further need be said. The more special and striking developments of mimetic resemblances are found in cases in which not merely the general color of their environments is imitated, but where resemblances of a close, and sometimes of a very extraordinary kind, to other animals, to plants, or even to inorganic objects, are to be noted. In the leaf-insects, which are included in the same order as locusts, crickets, etc., for example, the wings are not only colored to resemble leaves, but their structure imitates in the most exact manner the appearance of the veins of the leaf. Nor does the principle of imitation end with this sufficiently remarkable effect. In some leaf-insects the colors of the leaf-like wings actually change with the season of the year; as if in the most perfect sympathy and harmony with the alteration of colors in the actual leaves. And the mimicry becomes of still more perfect kind, to our thinking, when we find that the wings of the leaf-insect exhibit even the characteristic markings we are familiar with in leaves as produced by the attacks of minute insects; Nature thus imitating, not merely the natural structure of the leaf, but the very imperfections to which the leaf is subject. It has been suggested that the little leaf-eating insects may be themselves deceived by the mimicry of their larger neighbors, and may actually eat into the wings of the latter, and thus produce the eroded appearance. But, if this latter view be correct, it only makes out a stronger case for the perfect reproduction of the leaves in the wings of the insect. Mr. Wallace has given us a very typical example of another such case of the imitation, not only of leaves, but of the natural parasites of leaves, in a butterfly, the wings of which, on their under-surfaces, resemble leaves; while the imitations of decay of leaves and of the fungi that appear thereon are so close that, as Mr. Wallace remarks, "it is impossible to avoid
