THE ANIMAL AND ITS ENVIRONMENT 



721 



earth, the lithosphere. If the lithosphere were uniform in diameter, 

 it would be covered by a layer of water, the hydrosphere, which is 

 in turn surrounded by a gaseous layer, the atmosphere. It is only 



Fig. 376. — Diagram to show food relationships in a hypotlietical prairie com- 

 munity. (Redrawn and modifled from Shelford. Animal Communities in Temperate 

 America, published by University of Chicago Press.) 



--Lithosphere 



■-Hydposphere 



■-Atmosphere 



Fig. 377. — Diagram to show the relationship of the general areas of our planet. 



where the components of these three layers interact that life is pos- 

 sible. Living organisms cannot exist in the lithosphere (Fig. 377) 

 without the presence also of water, and of oxygen from the atmosphere. 

 Similarly life in water is possible only where it contains in solution 



