CHAP. II.] DISPERSAL AND MIGRATION, ll 
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 wherever 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. The 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 which the 
European ibex and moufion are striking examples. Rivers 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 absolutely 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 quadrumana appear to be limited by climate, 
