318 BACKBONED ANIMALS. 
the Mississippi region takes to the water when pursued, 
and swims and dives equally well. The jackass-rabbit 
(Z. callot’s) is remarkable for its long ears, while in the 
Alpine hare of the Rocky Mountains they are extremely 
short. Hares generally nest on the surface, while rabbits 
burrow. 
VaLuE.—Five million rabbit-skins are used annually in the fur- 
trade, and four and a half million hare-skins, 
NoTe.—The domestic varieties of rabbits have all sprung from the 
English variety. They live in bands, burrow, and are so prolific that 
it has been estimated that, under the most favorable circumstances, 
the progeny of a single pair in four years would amount to a million ! * 
Allied are the Cavies (Caviéde), found in South Amer- 
ica and the adjoining islands, seemingly taking the place 
of hares, the Agoutis, Guinea - pigs, the Capybara, the 
largest rodent, and the Paca, that forms burrows in the 
ground. Porcupines (Aystricidz).—These rodents (Fig. 
345) have the body and tail covered with stiff, rigid, barbed 
quills, from three to twelve inches in length. The molar 
teeth are sixteen in number, and the tongue is rough and 
armed with horny scales. They inhabit the temperate re- 
gions of the eastern and western hemispheres, living in 
burrows, and in the winter passing through a partial hiber- 
nation. The white-haired or Canada porcupine is nearly 
three feet long, including the tail. The spines are white, 
with darkened tips, the long hairs growing among them 
being similarly colored, and the fur a dark brown. They 
live upon bark and twigs, and also upon corn and various 
grains. The yellow-haired porcupine is much larger. 
The crested porcupine of Europe and Asia has spines 
a foot long; those upon the tail being hollow, open, and 
attached by slender pedicles. When not in use the spines 
lie flat, but are raised suddenly with a loud, crackling 
* Rabbits have increased so in certain parts of Australia that a 
famine is threatened. One colony has lost two thousand sheep from 
starvation, the rabbits having eaten up the grass. 
