THE SIMPLEST, OR ONE-CELLED ANIMALS 123 



As already learned in the examination of examples of 

 one-celled animals, it is evident that life may be success- 

 fully maintained without a complex body composed of 

 many organs performing their functions in a specialized 

 way. The marine Protozoa illustrate this fact admirably. 

 Despite their lack of special organs and their primitive 

 way of performing the life-processes, that they live success- 

 fully is shown by their existence in such extraordinary 

 numbers. They outnumber all other animals. The con- 

 ditions of life in the surface-waters of the ocean are easy 

 and constant, and a simple structure and simple method 

 of performing the necessary life-processes are wholly ade- 

 quate for successful life under these conditions. 



