ORDERS OF MAMMALIA. 337 
of the tooth acquires by use a chisel shape, bevelled away be- 
hind, and the enamel forms a persistent cutting edge. The Ro- 
dents are almost all of small size, and are very prolific. They 
subsist principally, if not entirely, on vegetable matters, espe- 
cially the harder parts of plants, such as the bark and roots. 
Many possess the power of building very elaborate nests, and 
most of them hybernate (z¢., remain torpid throughout the win- 
ter). They are very generally distributed over the whole world. 
The order Rodentia comprises a large number of families, of 
which little more than the names can be mentioned. The most 
important families of Rodents are the following : 1. Leforide, 
comprising the Hares and Rabbits. The Hares generally occur 
in temperate regions, but some are African, and one species 
occurs in the Arctic regions, while the common American Hare 
(Lepus Americanus) extends from Canada to Mexico. 2. 
Fig. 183.—Hamster (Cricetus vulgaris). 
Cavide, comprising the Capybaras, Guinea-pigs, &c. The 
Capybara is the largest of living Rodents, and is not unlike a 
small pig. It is anative of South America, and leads an amphi- 
bious life. Here also belong the Agoutis (Dasyfrocta) of South 
America and the West Indies, and the Pacas of South America. 
3. Hystricide, comprising the Porcupines, and characterised 
by the fact that the body is covered with longer or shorter 
spines or quills mixed with bristly hairs. Most of the Porcupines 
live in burrows, and are much like the Rabbits in their habits, 
but some are furnished with prehensile tails, and live in trees. 
4. Castorid@ or Beaver family, comprising the Beaver, Musquash, 
and Coypu. The Beaver has webbed feet and a scaly tail, and 
the fur is an article of considerable value. It inhabits both 
y 
