Page:Popular Science Monthly Volume 63.djvu/514

510 favorable attractive conditions, to escape more dominant forms outside, or simply by chance, from being carried in streams of water into these subterranean cavities, the result has been the same for all, and their return to the struggle carried on by their ancestors out of the question. They are distinct species modified and adapted to this particular environment where survival is possible, but opportunity for progressive evolution too limited to permit of advance.

Along the path of protective devices, mimicry, adaptive coloration, form and habit have traveled a host of different forms—flies that look like bumblebees and thereby gain entrance to their nests to provide extra food for their larvæ; butterflies that look like leaves of trees; leaf insects (phasmids) so like the leaves they live upon as to be invisible to foes; bugs that look like ants; scale insects that look like excrescences on the bark of the trees they infest; edible species that have taken form and color of inedible species; toads that look like lumps of earth; frogs that look like green scum or leaf at water side; snakes and lizards in great numbers that resemble the soil on which they live; birds that so closely imitate the colors of earth, foliage or irregularities of bark as to escape observation—in fact, an unending train in varying degrees, furnishing a most fascinating field for study.

Among aquatic animals we have fishes that hug close to the bottom and acquire color and pattern which admirably protect them, and the flounder has even gone to such an extreme in this direction as to have one of its eyes transferred from its normal position to the opposite side of the head. Skates and rays have the same flattening, but retain their normal position. Other fishes resemble rocks and so perfectly as to be practically invisible. Others, like sea horses, resemble parts of sea weed, streaming in the currents of water or branches of coral to which they cling. Mollusks and crustaceans adopt this plan to make themselves inconspicuous, and the different devices shown would fill a volume. Perhaps no stranger combination is presented than in the little crab which makes its home in a mollusk shell, but not content with this protection conspires with a sea anemone to take root upon its house top and add the variety of its structure to the deception. A queer sight these anemones, nodding here and there as borne by a hidden crab.

Most animals aside from man have been content to let electricity alone, and we are inclined to think the use of this magical force in nature of very recent origin. However, some of the aquatic animals, at least, and these forms that must have had their origin in the long, long ago of geological time, have brought to their use this elusive force and present in the structure of their organs for the generation of electricity some quite remarkable parallels to the electric apparatus of human invention. In such lines we have the torpedo, a broad, flat.