468 The Outline of Science 



special and adaptive use has been made of what was already 

 present apart from desert conditions altogether. More unique is 

 the development of a hump or of two humps, consisting chiefly 

 of fat. When the animal obtains for a time a considerable 

 quantity of moist herbage, the hump stands up tensely; when 

 supplies are scanty the hump is reduced in size and becomes 

 flabby. Another adaptation may be found in the Camel's power 

 of completely closing its nostrils during a sand-storm. 



Mountain Mammals 



Really great mountains often show three zones of forest, of 

 steppe-land with scanty vegetation, and of barren ground's or 

 tundra in the higher altitudes. Thus we find, among mountain 

 mammals, forest forms like Bears and some Monkeys, steppe 

 forms like Chamois and Yak, and tundra forms like Marmots and 

 Snow- Voles. Many of the mountain mammals are of very hardy 

 constitution, with thick fur, with great climbing powers, and with 

 a capacity for enduring severe conditions and a starvation diet. 

 Many are refugees from the low grounds, and some, like the 

 mountain beaver, are very old-fashioned, primitive types. 



The Mountain Hare 



The Variable or Mountain Hare is a first cousin of the 

 Common Hare, and is nowadays a distinctively northern mam- 

 mal. When the ice-sheet was thick over the mountains of Central 

 Europe the Variable Hare lived in the low grounds. When the 

 climate became milder it had to retreat either further north or 

 up the mountains. It became extinct in England, but has been re- 

 introduced with success. Compared with the Common Hare, it 

 is smaller as a whole, and in its head, ears, hind-legs, and tail; its 

 flesh is whiter; it is a less dainty feeder. It does not seem to have 

 any particular home or "form," but shifts about restlessly from 

 one hiding-place to another. When the snow is deep it is forced 

 to descend to lower levels. In Scotland it usually turns to white 



