12 INTRODUCTION 
Again, both in Asia and in North America we have 
vast areas of natural grassland forming well-defined 
Steppe areas, which possess a characteristic fauna. The 
great mountain chains of the earth’s surface are peopled 
by faunas having certain special features, and the vast 
area of coast-line which fringes the Arctic sea forms 
a cold desert or tundra, whose fauna has many pecu- 
liar features. As natural regions with a cold winter 
climate then, we have to consider (1) the Tundra, 
(2) the Taiga or coniferous forest, (3) the Steppe, best 
developed in the northern hemisphere, and (4) Mountain 
regions. ; 
Where the temperature is permanently high, and 
the precipitation great, we have (5) luxuriant Tropical 
Forest, with its characteristic fauna, differing according 
as the forest occurs in Africa, Asia, or South America, 
but showing in all cases certain special adaptations. 
Again, in warm or tropical regions where the tempera- 
ture is still high, but the rainfall small and unequally 
distributed throughout the year, we have a thinning of 
the forest into that type of grassland, or grassland 
mingled with wood, which the botanists call Savana. 
As the rainfall diminishes the savana thins out into 
desert, so that we may conveniently consider (6) 
Savanas and Warm Deserts together. 
This still leaves to be considered the fauna of (7) 
Islands, which show some special features, and also the 
animals of aquatic habitat, which we must consider 
separately, according as they live (8) in the sea, or 
(9) in fresh water. 
Such a scheme is obviously incomplete, in that it 
does not cover the whole surface of the globe. It 
omits, for example, any consideration of the fauna of 
the deciduous forest which covers so much ground in 
