332 MiaOELLANEOUS OBJECTIONS TO TEE 



to some other naturalists, that the Pleuronectidag are not 

 quite symmetrical even in the embryo; and if this be so, 

 wo could understand how it is that certain species, while 

 young, habitually fall over and rest on the left side, and 

 other species on the right side. Malm adds, in confirma- 

 tion of the above view, that the adult Trachypterus arcti- 

 cus, which is not a member of the Pleuronectidse, rests on 

 its left side at the bottom, and swims diagonally through 

 the water; and in this fish, the two sides of the head are 

 said to be somewhat dissimilar. Our great authority on 

 Fishes, Dr. Giinther, concludes his abstract of Malm's 

 paper, by remarking that "the author gives a very simple 

 explanation of the abnormal condition of the Pleu- 

 ronectoids." 



We thus see that the first stages of the transit of the 

 eye from one side of the head to the other, which Mr. 

 Mivart considers would be injurious, may be attributed 

 to the habit, no doubt beneficial to the individual and 

 to the species, of endeavoring to look upward with both 

 eyes, while resting on one side at the bottom. We may 

 also attribute to the inherited effects of use the fact of the 

 mouth in several kinds of flat-fish being bent toward the 

 lower surface, with the jaw bones stronger and more effect- 

 ive on this, the eyeless side of the head, than on the other, 

 for the sake, as Dr. Traquair supposes, of feeding with ease 

 on the ground. Disuse, on the other hand, will account 

 for the less developed condition of the whole inferior half 

 of the body, including the lateral fins; though Yarrel 

 thinks that the reduced size of these fins is advantageous 

 to the fish, as " there is so much less room for their action, 

 than with the larger fins above." Perhaps the lesser 

 number of teeth in the proportion of four to seven in the 

 upper halves of the two jaws of the plaice, to twenty-five 

 to thirty in the lower halves, may likewise be accounted 

 for by disuse. From the colorless state of the ventral sur- 

 face of most fishes and of many other animals, we may 

 reasonably suppose that the absence of color in flat-fish on 

 the side, whether it be the right or left, which is under- 

 most, is due to the exclusion of light. But it cannot be 

 supposed that the peculiar speckled appearance of the 

 upper side of the sole, so like the sandy bed of the sea, or 

 the power in some species, as recently shown by Pouchet, 



