PROTOZOA 



57 



neither nucleus nor contractile vacuole has been dis- 

 covered. Pelomyxa, a fresh-water form, may reach the 

 size of eight millimeters (.3 of an inch) in diameter. 



An amoeba is a naked fresh-water Rhizopod, contain- 

 ing a nucleus and a contractile vacuole, the body sub- 



FIG. i. Amoeba, showing the structure of the body and the changes which take place 

 during division. The dark body in each figure is the nucleus ; the transparent circle, 

 the contractile vacuole ; the protrusions of the body substance, pseudopodia ; the 

 outer, clear portion of the body, the ectosarc ; the granular portion, the endosarc ; 

 the granular masses, food vacuoles. Much magnified. 



stance consisting of two rather distinct layers, the outer 

 being quite clear and transparent, while the inner is usu- 

 ally filled with granules and ingested particles. During 

 movement the shape of the body is constantly changing, 

 owing to the protrusion and withdrawal of the pseudo- 



