Page:Popular Science Monthly Volume 6.djvu/537

Rh as we call them, which we now interpret as processes of evolution presenting certain definitely-marked stages, are, in the eyes of the primitive man, metamorphoses in the original sense. He accepts them as actual changes of one thing into another thing utterly different.

How readily the savage confounds these metamorphoses which really occur with metamorphoses apparently like them but impossible, we shall perceive on considering a few cases of mimicry by insects, and the conclusions they lead to. Many caterpillars, beetles, moths, butterflies, simulate the objects by which they are commonly surrounded. The Onychocerus scorpio is so exactly like, "in color and rugosity," to a piece of the bark of the particular tree it frequents, "that until it moves it is absolutely invisible:" thus raising the idea that a piece of the bark itself has become alive. Another beetle, Onthophilus sulcatus, is "like the seed of an umbelliferous plant;" another "undistinguishable by the eye from the dung of caterpillars;" some of the Cassidæ "resemble glittering dew-drops upon the leaves;" and there is a weevil so colored and formed that, on rolling itself up, it "becomes a mere oval brownish lump, which it is hopeless to look for among the similarly-colored little stones and earth pellets among which it lies motionless," and out of which it emerges after its fright, as though a pebble had become animated. To these examples given by Mr. Wallace, may be added that of the "walking-stick insects," so called "from their singular resemblance to twigs and branches."

What wonderful resemblances exist, and what illusions they may lead to, will be fully perceived by those who have seen, in Mr. Wallace's collection of butterflies, the Indian genus Kallima, placed amid the objects it simulates. Habitually settling on branches bearing dead leaves, and closing its wings, it then resembles a dead leaf, not only in general shape, color, markings, but in so seating itself that the processes of the lower wings unite to form the representation of a foot-stalk. When it takes flight, the impression produced is that one of the leaves has changed into a butterfly. This impression is greatly strengthened when the creature is caught. On the under side of the closed wings is still clearly marked the midrib, running right across them from foot-stalk to apex; and here, too, are lateral veins. Nay, this is not all. Mr. Wallace says: