AND DESERTS 123 
continents, though the species differ, the general facies 
is the same—tall grasses, thorny acacias, cactuses or 
cactus-like forms, and generally plants presenting 
special features which protect them against periodical 
drought, while allowing them to take advantage of the 
periodic tropical downfalls. 
Of the great savana regions of the world the African 
is especially rich in ungulates, notably in antelopes, 
the Australian in herbivorous marsupials, notably 
kangaroos and wallabies, while the savanas of South 
America, a country which has witnessed an extra- 
ordinary destruction of mammalian types in recent 
geological time, were relatively poor in mammalia till 
the advent of European man. 
One of the special climatic features of the savana 
proper is the periodic abundance of rain. As we pass 
from the savana to the desert the dry season increases 
in length, and the rain becomes less, and more un- 
certain. Vegetation also gradually diminishes as the 
conditions become less favourable, and the fauna 
becomes impoverished, the mammalian fauna diminish- 
ing first. In the desert proper few organisms can live, 
but the less unfavourable regions carry a reduced 
savana fauna, especially of insects and reptiles. The 
Kalahari, indeed, is said to serve as a reservoir for such 
insects as locusts, which breed there until starvation 
forces the swarms to sweep outwards to the better 
watered lands on the margin of the desert. 
No hard and fast line separates savana regions from 
steppes, this being especially true in South America, 
where the treeless ‘ pampas’ or steppes of the Argentine 
south of lat. 32° S. pass into a savana region further 
north. It should be noted, however, that in addition 
to the characters already given, typical savana regions 
