Now it is true that all beasts, birds, snakes, lizards, frogs, and fishes have some things alike, though each has some other things different from all the rest.

If they were not all alike in some things, we could not call them all animals.

One of the things in which all the animals I have named are alike is, that they all have skeletons.

One of the things in which all their skeletons are alike is, that they have backbones.
Backbones are the chains of bones that run along the back from the head to the tail.

Backbones are called by the Wise Men _vertebrae_; animals that have backbones are named _Vertebrates_; and animals that lack backbones are named _Invertebrates_." "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.