Page:Popular Science Monthly Volume 53.djvu/686

666 Lord Walsingham goes on to suggest that this intermittent display of bright coloring probably has as confusing an effect upon birds and other predaceous vertebrates as upon man; and that on this hypothesis such colors can be more satisfactorily accounted for than upon any other yet suggested.

This explanation is easy to understand and gives renewed emphasis to the oft-repeated statement that nothing in Nature is without significance. In the case of the Catocala moths one readily perceives that when driven to flight by a woodpecker or other bark-searching bird a moth which shows during a rapid irregular flight bright colors, and then alights, hiding the colors and instantly assuming entirely different hues, blending with the surroundings, would stand a better chance of escaping from a pursuing bird than a moth which had no bright colors with which to confuse the bird and prevent its seeing the place where the insect alights.

These insects are excellent illustrations of the combined action of the various forces which Darwin classed together under the term "natural selection." The factors involved are three—multiplication, variation, elimination. In nearly all organisms more young are produced than can mature. In these young there are infinite variations all directions. Some of these variations fit the individuals possessing them better to the conditions of life than variations in other directions. Consequently, the possessors of the latter will be eliminated in the struggle for existence and the former will escape elimination, and mature to reproduce. Their young will in part at least inherit the favorable variations, and thus have an advantage which will lead to their reproduction. Thus there is an ever-increasing tendency to a more perfect adaptation to environment.

On the rocky hills and sandy plains of New England there are several species of grasshoppers or locusts that also illustrate these principles. If you walk along a strip of sandy land in summer, you start to flight certain locusts which soon alight, and when searched for will be found closely to assimilate in color the sand upon which they rest. On a neighboring granite-ribbed hill you will find few if any of this species of locust, but instead there occur two or three