Page:Popular Science Monthly Volume 75.djvu/572

566, for instance, of concealing coloration, such as the transparency of a group of the supposed mimetics, have gone on, in this group, hand-in-hand with that of unpalatability. Now that we see that all procryptic coloration (except, of course, the facsimile kind, such as that of geometers) produces its effect by making the observer seem to see through the place where the colors are, it follows that actual transparency, as in these "mimetics," must, in ever so many situations, be wonderfully potent for obliteration. It is, of course, the only scheme for succeeding equally against both the light and the shadow, tending both to escape showing light against dark backgrounds and dark against light ones. Here are Bates's own remarks about the degree of conspicuonsness of a transparent butterfly. In "A Naturalist on the Amazons," on page 39, he writes:

Some have wings transparent as glass; one of these clear-wings is especially beautiful, namely, the Hetaera Esmeralda; it has one spot only of opaque coloring on its wings, which is of a violet and rose hue; this is the only part visible when the insect is flying low over dead leaves, in the gloomy shades where alone it is found, and it there looks like the wandering petal of a flower.

As a few hours' experimenting in obliteration by juxtaposition of patterns will prove to any student, the optical laws which govern it are so absolute that one is not surprised to find that the whole world's butterflies have scarcely three different schemes of pattern. The principle of pattern arrangement in these famous "mimetic" groups (shown in Fig. 6) is out and away the predominant one over the whole globe. If this is the case, is it strange that in each most swarmingly populated seat of butterfly life there prove to be a number of species which, living in the very same station, and with seemingly identical habits, have, in obedience to this great pattern-law, practically identical patterns and form? We see in the ocean, for instance, even mammals wearing the shape and color of fishes?

The question, now, is, at most, merely why they have the same station and habits.

Let us dwell a moment upon the significance of this finding of the greatest cryptic coloration in the very midst of the so-called mimetics. First we must remember that all men agree that it is only persecution that can have engendered any form at all of protection. It is, as I have said, inconceivable that any forever preyed-on and picked-from race should not have acquired all possible unpalatability. And it is equally inconceivable that any race that either preys or is preyed on should not during the same periods have become, also, as nearly as possible either invisible, or at least unrecognizable as any form of animal life. Such a boon incomparably surpasses any advantage from passing for some other at the best not wholly inedible animal. Therefore one would