56 GEOGRAPHICAL DISTRIBUTION. 



CHAPTER VII. 



GEOGRAPHICAL DISTRIBUTION. 



THE distribution of animals may be divided into 

 distribution in time and in space. The former is 

 usually termed Geological distribution, and in the latter 

 we may distinguish Geographical 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 terrestrial^ others again live in the sea or fresh- 

 water and are termed aquatic^ and yet others are found 

 spending most of their life in the air, these being termed 

 cerial. 



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 Jlora. 



Hence we can distinguish three primary habitats of 

 animals, called the terrestrial^ aquatic^ and ceriaL 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 aerial types must have 

 some form of wings or organs of flight. 



I. 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 (i) Marine and (2) Freshwater. 



(i) Marine Fauna. — The importance of the marine 

 fauna can hardly be over-estimated. The ocean has been 



