64 STEPPE FAUNAS AND TEMPERATE 
to modify the condition of the soil, so that special 
plants appear in the ‘marmot gardens’, which can 
thus be recognized from afar. The hemp-leaved nettle 
and wild rhubarb occur especially here, and the presence 
of the large leaves of these plants among the lyme 
grass (Elymus) of the steppes is a very obvious feature, 
while the loosening of the soil by the burrows makes 
progress for horsemen very difficult over the ‘ gardens ’. 
The interesting point is that rodents of similar habits 
seem to inhabit steppe regions in general. Thus the 
prairie marmot (Cynomys ludovicianus), a related form 
inhabiting the prairies of North America (Fig. 9), has 
similar habits, while the viscacha of the pampas of 
Argentina, though not very nearly related, shows also 
a general resemblance in habits, and also modifies the 
herbage in the regions of its occurrence. 
A different, though no less perfect, adaptation to 
steppe life is shown by the jerboas or jumping mice. 
In speaking of the marmots we noted that for rapid 
and efficient burrowing, short fore-legs are necessary, 
but, on the other hand, if the hind-legs are also short, 
the animal’s range of vision is small, and its speed 
cannot be great. On the other hand, if the legs are 
elongated to give speed, then feeding on the ground 
and drinking become difficult, as is seen in the giraffe 
(Fig. 36). The jerboas show a curious form of compro- 
mise to these varying needs, generally parallel to that 
shown by the kangaroo, which is, however, not a 
burrowing animal. In the jerboas the fore-limbs are 
short, thus permitting the animal to burrow, but the 
hind-legs are enormously long (Figs. 37 and 38), and the 
tail also long and capable of helping in the support of 
the body. The animal therefore progresses by leaps, the 
fore-legs not touching the ground at all. In feeding, 
