Hence,
soon growing tired, they fall to the bottom on one side. While thus at
rest they often twist, as Malm observed, the lower eye upward, to see above
them; and they do this so vigorously that the eye is pressed hard against
the upper part of the orbit. The forehead between the eyes consequently
becomes, as could be plainly seen, temporarily contracted in breadth. On
one occasion Malm saw a young fish raise and depress the lower eye through
an angular distance of about seventy degrees.
We should remember that the skull at this early age is cartilaginous and
flexible, so that it readily yields to muscular action. It is also known
with the higher animals, even after early youth, that the skull yields and
is altered in shape, if the skin or muscles be permanently contracted
through disease or some accident. With long-eared rabbits, if one ear
flops forward and downward, its weight drags forward all the bones of the
skull on the same side, of which I have given a figure. Malm states that
the newly-hatched young of perches, salmon, and several other symmetrical
fishes, have the habit of occasionally resting on one side at the bottom;
and he has observed that they often then strain their lower eyes so as to
look upward; and their skulls are thus rendered rather crooked. These
fishes, however, are soon able to hold themselves in a vertical position,
and no permanent effect is thus produced.
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