PROTOZOA 



131 



Wastes. — The constant activity of these animals in- 

 volves constant disintegration of protoplasm, and new- 

 protoplasm to take its place must be constantly made 

 from the food substances. This involves a series of 



Fig. 73.— Ameba after a full meal, consisting of a large diatom (dt) ; n, nucleus ;f.v. 

 food vacuoles ; c.v., contractile vacuoles. (From Sedgwick and Wilson, after 

 Leidy.) 



chemical actions. Complex unstable substances disin- 

 tegrate and new unstable substances are built up and in 

 the process stable substances are formed. These stable 

 substances can no longer be used by the body either for 

 the manufacture of protoplasm or for the production of 

 heat. They are therefore given off as wastes. The 

 principal wastes are carbon dioxide and water vapor 



