"Tell us the names of some Invertebrates, please, Doctor," said Rap.
"Well, all sorts of insects are Invertebrates, and so are lobsters and crabs, oysters and clams, worms, starfishes, jelly-fishes, corals, and even sponges. Then there are some too small to see without a microscope. But never mind about Invertebrates now. I only want you to remember that all beasts, birds, reptiles, and fishes are Vertebrates, and that there are five principal classes of them. If I should tell you as much about them as I have about the Building of a Bird, you would see that they are all built on what we call the Vertebrate plan of structure. Here is a chart of the Classes of Vertebrates—you can study it this afternoon, till you learn it by heart."
VERTEBRATES
Animals with Backbones
CLASS I. Mammals.—Warm-blooded animals which have fur or hair, bring forth their young alive, and nurse them. House People are Mammals.
CLASS II. 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.