342 



BIOLOGY OF THE PROTOZOA 



may be postponed in Protozoa by reorganization processes. In 

 many-celled animals, however, these cannot be applied, the more 

 the life of the single cell depends on the total organization/' 

 (Hertwig, 1914, p. 580.) 



II. HEREDITY AND VARIATIONS IN PROTOZOA. 



Owing to the relative simplicity of the organisms with which we 

 are dealing there are few structural characteristics that can be used 

 in a study of variations. Variations in size are often noted but 



3)0 



Fig. 167. — Size variations in eight families of Paramecium. (After Jennings.) 



these in themselves do not furnish reliable data, a Bileptiis gigas for 

 example may be 250 microns in length or only 25 microns (Fig. 6, 

 p. 27) according to the food it gets. Similar differences due to 

 temporary conditions are evident in all organisms that are studied 

 for a sufficient length of time. In a mixed population, however, 

 size differences may indicate fixed variations as was clearly shown 

 by Jennings (1909) for Paramecium (Fig. 167). 



