Birds .-- Warm-blooded animals which have feathers and lay eggs.
CLASS III.

Reptiles .-- Cold-blooded animals which have scaly skins, like lizards, snakes, and turtles.
CLASS IV.

Batrachians .-- Cold-blooded animals which have naked skins, like frogs, toads, and newts.
All the foregoing classes, except a few of the Batrachians, breathe air in lungs, and almost all, except snakes, have legs; none now living can fly, except bats and birds; but bats are Mammals.
CLASS V.Fishes .-- Cold-blooded animals which have either scaly or naked skins, but no fur or feathers; which live in the water, breathe it with their gills, and swim in it with fins..