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CHAPTER V

FISHES

THE fishes form the lowest class of vertebrated
animals. They all have gills, by which they breathe
the oxygen in the water, and they all breathe ex-
clusively by gills, except one order of them, in which
the air-bladder is used as a lung. It is now cus-
tomary to divide the class into four orders: the
teleostean, or bony fishes, to which the great bulk
of our food fishes belong; the ganoid, or armoured
fishes, like the sturgeon; the dipnoid, or mud-fishes,
the double-breathers, like the Queensland barra-
munda; and the cartilaginous fishes, like the sharks
and rays.

TELEOSTEI—If we say that these are the
typical fishes, like the perch, it will save us a lengthy
definition. They are conveniently divisible into six
groups, of which the perch, the wrasse, the turbot,
the salmon, the sea-horse, and the globe-fish may be
taken as representatives. They all of them, except
the last, have comb-like gills. The first four have
movable upper jaws; the first two have spinous rays
on the fins, the next two have no spinous rays; in