12 



ANIMAL LIFE 



now simply divides in two, and a large number of genera- 

 tions by simple fission follow. 



Paramwcium in the character of its body and in the 

 manner of the performance of its life processes is distinctly 

 less simple than the Amoeba, but its body is composed of a 

 single structural unit, a single cell, and it is truly one of 

 the " simplest animals." 



6. Vorticella. Another interesting and readily found 

 protozoan is Vorticella (Fig. 8). While the Amoeba can crawl 

 and ParamoBcium swim, Vorticella, except when very young, 



FIG. 8. VorticeUa microstoma (after STEIN). A, small, free-swimming individuals 

 conjugating with a large, stalked individual ; B, a stalked individual dividing 

 longitudinally ; C, after division is completed one part severs itself from the 

 other, forms a ring of cilia, and swims away. 



is attached by tiny stems to dead leaves or sticks in the 

 water, and can change its position only to a limited extent. 



