AND DESERTS 135 
to cold or wet. Another species is found in Bolivia. 
The members of the type genus Dasypus are widely 
distributed, being especially common in the Argentine. 
In addition to the protective covering of bony plates, 
they find security from their enemies in their burrow- 
ing habits, and in the fact that they are mostly noc- 
turnal. 
In Africa, where armadillos are completely absent, 
another curious edentate, the aard-vark or ant-bear 
(Orcyteropus) occurs in open regions, and is also of 
burrowing nocturnal habits, though it has no armour 
as the armadillos have. It seems to feed chiefly on 
termites, the so-called white ants. 
Of the marsupials the kangaroos and their immediate 
allies are exclusively confined to the Australian region, 
and there they formed the natural fauna of the savanas 
till the advent of the European with his flocks and 
herds. The kangaroos and wallabies, with the excep- 
tion of the tree-kangaroos already mentioned, are 
ground forms, feeding not only upon grass but also 
upon shoots of bushes and shrubs, or even in the case 
of the larger forms, on leaves, &c., of trees, which they 
reach by standing in the upright position. The tail is 
long and strong. It aids the animal in maintaining 
the upright position, and also in running—that is, in 
leaping. We have already noticed the essential points 
of structure in the kangaroo; the elongation of the 
hind-limbs, without corresponding elongation of either 
forelimbs or neck, is an adaptive peculiarity which is 
far from uncommon in animals of the open plains. In 
the ungulates the other type of adaptation, that which 
consists in the elongation of both pairs of limbs, and 
therefore necessarily of the neck to permit feeding to 
take place, is the usual one. Just as among the rodents 
