n 4 THE POPULAR SCIENCE MONTHLY. 



fish. Some have taken to lying most frequently on one side and some 

 on the other ; but it is interesting to note that when a normally right- 

 sided individual has happened to lie with his left side uppermost that 

 side becomes colored and distorted exactly the same as in his more cor- 

 rect brethren. This shows how purely acquired the whole habit must 

 be. It points back clearly to the days when flat-fish were still merely 

 a sort of cod, and suggests that their transformation into the un sym- 

 metrical condition is merely a matter of deliberate choice on their own 

 part. Indeed, there seems good reason to believe that many young 

 flat-fish never undergo this change at all, but swimming about freely 

 in the open sea assume that peculiarly elongated and strange form 

 known as the leptocephalic. 



I don't mean to say that all leptocephali are originally the offspring 

 of flat-fishes, but some probably are ; and so a word or two about these 

 monstrous oceanic idiots and imbeciles may not be here out of place. 



Lolling about lazily in the open ocean a number of small, long, rib- 

 bon-like fish are frequently found, quite transparent and glassy in ap- 

 pearance, with no head at all to speak of, but furnished with a pair of 

 big eyes close beside the tiny snout. They are languid, boneless, worm- 

 like creatures, very gelatinous in substance, and looking much like pel- 

 lucid eels without the skin on. For a long time these leptocephali (as 

 they are called) were supposed to be a peculiar class of fishes, but they 

 are now known to be young fry of various shore-haunting kinds, which 

 have drifted out into the open ocean, and had their development per- 

 manently arrested for want of the natural environment. They are in 

 fact fish idiots, and though they grow in size they never attain real 

 maturity. If, as some authorities believe, many of these queer idiotic 

 forms really represent stray flat-fish, then their symmetrical develop- 

 ment once more points back to the happy days when the ancestral sole 

 still swam upright, with one eye on each side of his head, instead of 

 being distorted into a sort of aggravated squinter. 



Besides the " reversed " specimens of soles and turbots right-sided 

 when they ought to be left-sided, and vice versa occasional double or 

 ambidextrous individuals occur, in which the dark color is equally de- 

 veloped on both sides of the body. Whether these impartial flat-fish 

 are in the habit of turning over in their beds whether they represent 

 the uneasy sleepers of pleuronectid circles or otherwise I am not in a 

 position to state ; but probably they are produced under circumstances 

 where both sides have been frequently exposed to the action of light, 

 which seems to have a sort of photographic effect upon the pigments 

 of the fish's body. Everybody knows in fact that the upper side or 

 back of most ordinary fish, exposed as it is to the sunlight, is darker 

 than the lower side or belly ; and this natural result of the solar rays 

 has indirectly a protective effect, because when you look down into 

 the water from above it appears dark, whereas when you look up from 

 below the surface appears bright and shining ; so that a fish is less 



