CHAP. II.] DISPERSAL AND MIGRATION. 11 



stopped by any physical obstacles. The elephant is almost 

 equally at home on plains and mountains, and it even climbs to 

 the highest summit of Adam's Peak in Ceylon, which is so steep 

 and rocky as to be very difficult of ascent for man. It traverses 

 rivers with great ease and forces its way through the densest 

 jungle. There seems therefore to be no limit to its powers of 

 wandering, but the necessity of procuring food and its capacity 

 of enduring changes of climate. The tiger is another animal with 

 great powers of dispersal. It crosses rivers and sometimes even 

 swims over narrow straits of the sea, and it can endure the 

 severe cold of North China and Tartary as well as the heats of 

 the plains of Bengal. The rhinoceros, the lion, and many of the 

 ruminants have equal powers of dispersal ; so that wlierever there 

 is land and sufficient food, there are no limits to their possible 

 range. Other groups of animals are more limited in their migra- 

 tions. Tlie apes, lemurs, and many monkeys are so strictly 

 adapted to an arboreal life that they can never roam far beyond 

 the limits of the forest vegetation. The same may be said of 

 the squirrels, the opossums, the arboreal cats, and the sloths, with 

 many other groups of less importance. Deserts or open country 

 are equally essential to the existence of others. The camel, the 

 hare, the zebra, the giraffe and many of the antelopes could not 

 exist in a forest country any more than could the jerboas or the 

 prairie marmots. 



There are other animals which are confined to mountains, and 

 could not extend their range into lowlands or forests. The goats 

 and the sheep are the most striking group of this kind, inhabit- 

 ing many of the highest mountains of the globe ; of whicli the 

 European ibex and mouflon are striking examples. Eivers are 

 equally necessary to the existence of others, as the beaver, otter, 

 water-vole and capybara ; and to such animals high mountain- 

 ranges or deserts must form an a1)solutely impassable barrier. 



Climate as a Limit to the Range of Mammals. — Climate appears 

 to limit the range of many animals, though there is some reason 

 to believe that in many cases it is not the climate itself so much 

 as the change of vegetation consequent on climate which produces 

 the effect. The quadnmiana appear to be limited by climate, 



