More than two-thirds of our globe being covered by the waters of
the ocean, and of the remaining third a great part being washed by
extensive rivers, or occupied by lakes, ponds, or marshes, these
watery realms, teeming with life, furnish man with a great variety of
food. Some of these have already passed under consideration in the
reptilia, and others in the great class mammalia, as seals, morses, and
manatees, which can remain at no great distance from the sea, together
with whales, which never leave it, though constantly obliged, by the
nature of their respiration, to seek its surface.
Mollusca, crustacea, annelides, and zoophytes are almost peculiar to
this element, having but few scattered representatives on earth; but,
amidst all its varied inhabitants, there are none more exclusively
confined to its realms, none that rule them with such absolute sway,
none more remarkable for number, variety of form, beauty of colour,
and, above all, for the infinite advantages which they yield to man,
than the great class of fishes. In fact, their evident superiority
has caused their name to pass as a general appellation to all the
inhabitants of the deep. Whales are called fish, crabs are called
shell-fish, and the same term is used to denote oysters; though the
first are mammalia, the second articulata, and the third mollusca.