154 



REPRESENTATIVE SINGLE-CELLED ANIMALS 



{cj. p. 241). The scheme most commonly used separates them 

 into the four groups indicated in the following paragraphs. 



Fig. 84. — Representatives of the four classes of protozoa. 



A, Amoeba, Class Sarcodinj,. B, Chilomonas, Class Mastigophora. C, Frontonia, Class 

 Infusoria. D, Pudophrya feeding on small ciliate, Class Infusoria. E, Gregarina attached 

 to cell of host's intestine and stages within such cells, Class Sporo^oa. 



Class Sarcodina. — These are forms in which the cell exhibits 

 more or less temporary processes termed pseudopodia, or "false 

 feet." In one subdivision, the Rhizopoda (Fig. 84 A), which are 

 typically creeping forms, these processes are k)bed or root-like and 

 sometimes branching. In another, the Actinopoda, which are 

 typically floating forms hke Actinophrys (Fig. 85), the pseudo- 

 podia are stiff and more permanent. The name Sarcodina was 

 originally applied to this class of the protozoa, because of their 

 resemblance to the sarcode or "flesh/' as the protoplasm of animal 

 cells was called in the early days of the cell theory. 



Class Mastigophora. — In these forms the cell possesses, in 

 the dominant phase of its hfe cycle, one or more flagella, or 

 whip-like processes, which are used for locomotion, and in some 

 instances for feeding. The number of flagella is relatively small. 

 The Mastigophora (Fig. 85) are a very diversified group, repre- 



