Some Naturalists claim that these are the only inhabitants of the water
that should be called Fishes—that the Cetacea or the Whale family are
simply huge beasts that have taken up their abode in the ocean, and that
the cartilagenous Fishes form an amphibious band by themselves.
Others have classed the whole of these three great groups under the name
of Fishes. But modern Scientists have settled upon the classification
which has been carried out in this little Natural History—the Cetacea
are placed among the Mammals and kept entirely distinct from the Fishes
(none of which feed and care for their young in the same manner as the
Mammals); and the great tribe of Fishes are now divided into two groups
of cartilaginous and osseous Fishes, with their numerous sub-divisions
into families and species.
We have studied the curious families of the cartilaginous Fishes and now
we find more familiar varieties of our well-known Fishes among the
families of bony Fishes, although even in this division some very rare
and wonderful specimens are found.
The history of any one family of the bony Fishes very closely resembles
all the rest—they breathe air and water through the gills. They live by
devouring such Fish and the animal life of the great waters as their
mouth is capable of admitting. They propagate not by bringing forth
their young alive, like the Mammals and a few of the cartilaginous
Fishes, nor by distinct eggs, like the remainder of the latter class,
but by spawn, as their roe is called, which is made up of hundreds, and
in some instances hundreds of thousands of tiny eggs.
The bones of these Fishes also makes them distinct from all others. They
have the appearance of being solid, but when examined more closely they
are found to be hollow and filled with a substance less oily than
marrow. These bones are very numerous and pointed and to them the
muscles are fixed which move the different parts of the body.