456 
MAMMALIA. 
more striking. The tail is long and covered with short hair, 
and terminated by a tuft ; the coat is soft and thick. 
The J erhoa inhabits the vast solitudes of Africa, and the steppes 
of Tartary and Eussia. They dig out burrows, in which they 
pass the day, sleeping on a bed of grass and moss. But in the 
evening they seek their food, which consists of roots and seeds. 
They make use of their fore paws to convey what they eat to their 
mouths. 
Under ordinary circumstances, when nothing occurs to hurry or 
excite them, the Jerboas walk on all fours ; but if, from the 
scarcity of sustenance, or the necessity of escaping from danger, 
they are compelled to go a considerable distance in a short 
space of time, they use their hind legs only, moving forward in 
leaps, like the Jerboa-Eats ; hut the span of their bounds is of 
much greater extent, reaching sometimes to three yards. The 
way in which these springs are made is very curious. The 
animal first crouches down on its tarsi, at the same time stretch- 
ing out and stiffening its tail, so as to make another hearing- 
point on the ground ; then, suddenly, it hounds forward, as if 
forced hy a spring. The same manoeuvre is repeated after an 
imperceptible interval of time. It is said that the Jerboa can 
compete in. speed with a fast horse. The ancients, looking at 
this peculiar mode of progression, were led to think that the 
fore legs of these Eodents were absolutely unfitted for walking, 
and for this reason gave them the name of Dipus, which signifies 
two-footed. 
Jerboas are difficult to tame ; they can, however, be kept in 
cages ; and the menagerie of the J ardin des Plantes at Paris is in 
possession of several specimens. It is necessary to place them in 
cages made of iron wire, for the hardest wood cannot resist 
their jaws. Their size varies from that of the Mouse to that of 
the Brown Eat. 
Among the numerous species which are known, we will mention 
one which is common in Algeria, especially in the province of 
Oran, the Alactaga, called also by the significant name of Sagitta, 
or Arrow, which is also a native of Southern Eussia and some 
parts of Asia. 
The Pedetes Genus . — The Great Jerboa, or Jumping-Hare, or 
Spring-Hare of the Colonists, and Helamys, are the representa- 
