24 THE ANIMAL KINGDOM. 



Mammalia.* The flesh-eating animals have front teeth, 

 which they can strike into their prey like so many sharp 

 hooks, whilst their back teeth work against each other 

 like the blades of strong shears, and so cut up their 

 food. Those animals which live on grass and herbage 

 have sharp, flat, front teeth, which work against a pad in 

 the upper lip, and cut off the grass close to the ground, 

 something like a carpenter's adze f takes off chips ; and 

 the back teeth, which arc broad and flat, are made to 

 move horizontally over each other by a lateral (or side- 

 way) motion of the jaw, which you have no doubt noticed 

 in cows and horses. In squirrels, beavers, c., the front 

 teeth are like chisels, and not only continue growing, 

 but, by a peculiar formation, they keep constantly sharp, 

 however much the little carpenter may use his tools, and 

 however hard the wood may be in which he has to work. 

 Thus, the squirrel can cut through the shells of nuts, the 

 beaver can chop down branches of trees, whilst their back 

 teeth rub over each other just like a pair of rasps or rough 

 files. 



The feet of Mammalia, too, are adapted to their various 

 modes of life. Thus, the camel has broad, spongy soles, 

 which enable it with comfort to tread the sandy desert, 

 and has pads on its limbs, on which it rests when it 

 kneels ; the lion has strong, terrible claws, by which he 

 can catch his prey ; the monkey has all his feet formed 

 like hands, by which he is enabled to grasp the branches 

 of trees in climbing ; whilst in the horse and other animals 

 adapted for walking on firm soil or bearing burdens, the 

 feet are enclosed in hoofs, which form natural shoes. 



The feet and teeth, then, are points upon which classifi- 

 cation is mainly based, since these are always found 

 to be adapted to the special requirements of the animal. 



* .See " Our Bodies," page 44. 



t " Our Houses," Casscll's Primary Series, Fig. 32. 



