Page:Popular Science Monthly Volume 9.djvu/379

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357
ANIMAL POWERS OF OFFENSE AND DEFENSE.

thinking at first sight that the "butterflies themselves have been attacked by real fungi."

The walking-stick insects, as they are called, in their turn imitate, in the skeleton-like structure of their bodies, the appearance of dried twigs; and it is a singular fact that even in their awkward, ungainly manner of walking, the resemblance to the chance movements of twigs is clearly perceptible; the mimicry being rendered more realistic through this latter phase. Then, also, we find certain harmless groups of moths imitating closely the outward appearance of species of stinging bees and hornets. And one remarkable case of mimicry is the well known instance of some perfectly inodorous South American butterflies, which perfectly reproduce the external appearance of other butterflies which emit a most offensive odor; the reason assigned for this latter phase of mimicry being the very feasible one that the inodorous forms are protected from the attacks of birds by their resemblance to their strong-smelling neighbors. As a last instance of this curious phase of animal organization, we may note the example furnished by those curious little fishes, the Hippocampi, or sea-horses—so named from the obvious resemblance of the form of the head to that of a horse—the bodies of which become covered with long streamers of certain kinds of seaweed; so that, when these fishes rest amid the seaweed-covered nooks of their marine grottoes, the presence of their streamers serves to render detection by their enemies no easy matter.

Referring to the explanation, if such can be afforded, of these mimetic resemblances, there can be little doubt that, viewed as to its ultimate use and purpose, the condition of mimicry serves in the most effective manner as a means of defense and protection to the animals so endowed. The resemblance of the colors of birds to that of their habitat presents an obvious instance of this purpose; as also does the more complicated example of the imitation, by scentless butterflies, of their odorous neighbors. But, as regards the exact means whereby the condition of mimicry is induced and perfected, or concerning the exact causes of its assumption and development, natural history science, in its practical aspect, remains silent; although the bolder march of theory and speculation may indeed lead us for a little way toward the solution of the problem. At any rate, there can be no difficulty to our clearly appreciating the workings of a great law of purpose and design in the production of mimicry, as serving to protect the weak and less powerful against stronger and better-provided animals.

Turning now to some lower forms of animal life, we find in such forms as the Hydrœ, or common fresh-water polyps, the zoöphytes, sea-anemones, jelly-fishes, and allied forms, excellent examples of very specific means of defense and offense in animals. Within the tissues of the bodies of the foregoing organisms, when these tissues are microscopically examined, numerous little sacs or cells, varying in size