Fishes without exception are supplied with blood. Some of them are
oviparous, and some viviparous; scaly fish are invariably oviparous,
but cartilaginous fishes are all viviparous, with the single exception
of the fishing-frog.

Of blooded animals there now remains the serpent genus. This genus
is common to both elements, for, while most species comprehended
therein are land animals, a small minority, to wit the aquatic
species, pass their lives in fresh water. There are also sea-serpents,
in shape to a great extent resembling their congeners of the land,
with this exception that the head in their case is somewhat like the
head of the conger; and there are several kinds of sea-serpent, and
the different kinds differ in colour; these animals are not found in
very deep water. Serpents, like fish, are devoid of feet.