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. For had they been able to seize their prey more
easily than they do, they would soon have perished from
over-repletion. An additional reason is that the projecting
extremity of the head in these fishes is round and small, and
therefore cannot admit of a wide opening.
Again, even when the mouth is not placed on the under surface, there
are differences in the extent to which it can open. For in some
cases it can gape widely, while in others it is set at the point of
a small tapering snout; the former being the case in carnivorous
fishes, such as those with sharp interfitting teeth, whose strength
lies in their mouth, while the latter is its form in all such as are
not carnivorous.
The skin is in some fishes covered with scales (the scale of a
fish is a thin and shiny film, and therefore easily becomes detached
from the surface of the body). In others it is rough, as for
instance in the Rhine, the Batos, and the like. Fewest of all are
those whose skin is smooth. The Selachia have no scales, but a rough
skin. This is explained by their cartilaginous skeleton. For the
earthy material which has been thence diverted is expended by nature
upon the skin.
No fish has testicles either externally or internally; as indeed
have no apodous animals, among which of course are included the
serpents. One and the same orifice serves both for the excrement and
for the generative secretions, as is the case also in all other
oviparous animals, whether two-footed or four-footed, inasmuch as they
have no urinary bladder and form no fluid excretion
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