reasing
flatness of their bodies, and a permanent effect is thus produced on the
form of the head, and on the position of the eyes. Judging from analogy,
the tendency to distortion would no doubt be increased through the
principle of inheritance. Schiodte believes, in opposition to some other
naturalists, that the Pleuronectidae are not quite symmetrical even
in the embryo; and if this be so, we 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 confirmation
of the above view, that the adult Trachypterus arcticus, which is not a
member of the Pleuronectidae, 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. Gunther, concludes his abstract of Malm's paper, by
remarking that "the author gives a very simple explanation of the
abnormal condition of the Pleuronectoids."

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 endeavouring 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 towards the lower surface, with the jaw bones
stronger and more effective 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 colourless state of
the ventral surface of most fishes and of many other animals, we may
reasonably suppose that the absence of colour 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 c