12 ANIMAL LIFE 
now simply divides.in two, and a large number of genera- 
tions by simple fission follow. 
Paramecium in the character of its body and in the 
manner of the performance of its life processes is distinctly 
less simple than the Ameba, 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 Amwbda can crawl 
and Paramecium swim, Vorticella, except when very young, 
Fra. 8.—Vorticella 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. 
