Page:Popular Science Monthly Volume 29.djvu/120

110 ; in other words, she has managed it by the soles with swim-bladders being always promptly devoured. Originally, we may well suppose, the ancestral sole, before he began to be a sole at all (if I may be permitted that frank Hibernicism), possessed this useful aërostatic organ just like all other kinds of fishes. But when once he took to larking on the bottom and trying to pass himself off as merely a bit of the surrounding sand-bank, the article in question would obviously be disadvantageous to him under his altered circumstances. A bit of the sand-bank which elevates itself vertically in the water on a couple of side-fins is sure to attract the unfavorable attention of the neighboring dog-fish, who love soles like human epicures. Accordingly, every aspiring sole that ever sought to rise in the world with undue levity was sure to be snapped up by a passing foe, who thus effectually prevented it from passing on its own peculiar aspirations and swim bladder to future generations. On the other hand, the unaspiring soles that hugged the bottom and were content to flounder along contentedly sidewise, instead of assuming the perpendicular, for the sake of appearances, at the peril of their lives, lived and flourished to a good old age, and left many successive relays of spawn to continue their kind in later ages. The swim-bladder would thus gradually atrophy from disuse, just as always happens in the long run with practically functionless and obsolete organs. The modern sole bears about perpetually in his own person the mark of his unenergetic and sluggish ancestry.

At the same time that the young sole, setting up in life on his own account, begins to lie on his left side only, and acquires his adult obliquity of vision, another singular and closely correlated change begins to affect his personal appearance. He started in life, you will remember, as a transparent body; and this transparency is commonly found in a great many of the earliest and lowest vertebrate organisms. Professor Ray Lankester, indeed, who is certainly far enough from being a fanciful or imaginative person, has shown some grounds for believing that our earliest recognizable ancestor, the primitive vertebrate? now best represented by that queer little mud-fish, the lancelet, as well as by the too famous and much-abused ascidian larva, was himself perfectly translucent. One result of this ancient transparency we still carry about with us in our own organization. The eye of man and of other higher animals, instead of being a modification of the skin (as is the case with the organ of vision in invertebrates generally), consists essentially of a sort of bag or projection from the brain, turned inside out like the finger of a glove, and made by a very irregular arrangement to reach at last the outside of the face. In the act of being formed, the human eye in fact buds out from the body of the brain, and gradually elongates itself upon a sort of stalk or handle, afterward known as the optic nerve. Professor Lankester suggests, as a probable explanation of this quaint and apparently rather roundabout