56 GEOGRAPHICAL DISTRIBUTION. 
CHAPTER VII. 
GEOGRAPHICAL DISTRIBUTION. 
HE distribution of animals may be divided into 
distribution in time and in space. The former is 
usually termed Grotocicat distribution, and in the latter 
we may distinguish GEocRAPHICAL distribution, divided into 
Physical and topographical. 
Physical Distribution.—If we take note of the place 
of animals in nature we see at once that some inhabit the 
land and are zevrestrial, others again live in the sea or fresh- 
water and are termed aguatic, and yet others are found 
spending most of their life in the air, these being termed 
@rial, 
The aggregate of animals which are found in one of 
these particular habitats is termed the fauna of the habitat, 
just as that of plants constitutes the flora. 
Hence we can distinguish three primary Aaditats of 
animals, called the ‘ferrestrial, aquatic, and e@rial. The 
fauna of any one of these may be very diverse and be made 
up of animals differing widely from each other in many 
respects, but still we shall be able to notice that connected 
with each habitat there are certain main structural features 
in the fauna, For example, all the erial types must have 
some form of wings or organs of flight. 
1. Aquatic Fauna.—In this fauna are included the 
inhabitants of the ocean, of our seas, lakes, rivers, streams, 
and ponds. 
With such an enormous diversity of physical conditions, 
there are few general features to be discerned. We may at 
once divide it into (1) Marine and (2) Freshwater. 
(1) Marine Fauns.—The importance of the marine 
fauna can hardly be over-estimated. The ocean has been 
