192 A COUNTRY READER. 



and spiders. The caterpillars of many of the 

 species that they destroy are very injurious to 

 agriculture and forestry. 



Gnawing Animals. 



All the gnawing animals have four long teeth, 

 called incisor teeth, the crowns of which are 

 continually being worn down ; but in order that 

 they should not be worn away altogether, a growth 

 corresponding to the loss takes place at the root 

 end. 



Gnawing wears down these teeth less in front 

 than *behind. Their crowns therefore are always 

 sharp like a chisel edge. 



The large incisor teeth are used for gnawing, 

 in which process the lower jaw is moved back- 

 wards and forwards. 



Hares, rabbits, rats, and mice are all gnawing 

 animals. 



Hares and rabbits are so well-known to you 

 that there is no need to give any details about 

 their life history. 



The Mouse Family. The larger members of 

 the mouse family are called rats, and are often 

 confused with the vole family, but they are 

 really very different in appearance. 



The mouse family includes the black, and 

 brown rats, the common mouse, the long-tailed 

 field mouse, the harvest and corn mouse. 



