no THE POPULAR SCIENCE MONTHLY. 



tion ; in other words, she has managed it by the soles with swim-blad- 

 ders being always promptly devoured. Originally, we may well sup- 

 pose, the ancestral sole, before he began to be a sole at all (if I may 

 be permitted that frank Hibernicism), possessed this useful aerostatic 

 oreaii iust 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 neigh- 

 boring 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 con- 

 tentedly 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 per- 

 petually 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 ob- 

 liquity of vision, another singular and closely correlated change begins 

 to affect his personal appearance. He started in life, you will remem- 

 ber, as a transj^arent body ; and this transparency is commonly found 

 in a great many of the earliest and lowest vertebrate organisms. Pro- 

 fessor Ray Lankester, indeed, who is certainly far enough from being 

 a fanciful or imaginative person, has shown some grounds for believ- 

 ing 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 arrange- 

 ment 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 proba- 

 ble explanation of this quaint and apparently rather roundabout ar- 



