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.