THE BUILDING OF A BIRD 47 



are lobsters and crabs, oysters and clams, worms, star- 

 fishes, jelly-fishes, corals, and even sponges. Then 

 there are some too small to see witliout a microscope. 

 But never mind about Invertebrates now. I only want 

 you to rememl)er 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 Verte- 

 brate 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 icith 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 



^ I animals. 

 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. 



