12 ANIMAL FORMS 
14. The Ameba,—Among the simplest one-celled ani- 
mals living in the ooze at the bottom of nearly every fresh- 
water stream or pond is the Amwda (Fig. 5, A), whose body 
is barely visible to the unaided eye. Under the microscope 
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Fie. 5.—A, the Amada, highly magnified, showing c.v., pulsating vacuole; f, food 
particle ; 2, nucleus, The arrows show the direction of movement. B, shape of 
same individual 30 seconds later, C, an ameeba-like animal (Digiugia) partially 
enclosed inashell. D,an Ameba in the process of division. E, Gromia, another 
shelled protozoan (after SCHULZE). 
it is seen to consist of an irregular, jelly-like mass of proto- 
plasm totally destitute of a cell wall. Unlike those animals 
with which we are familiar, the body constantly changes its 
shape. A rounded bud-like projection will be seen to appear 
on one side of the body and the protoplasm of adjacent 
regions flows into it, thereby increasing its extent. Similar 
projections at the opposite end of the cell are withdrawn, 
and their substance may flow into the newly formed lobe, 
which gradually swells in size and pushes forward. Thus, 
by constantly advancing the front part of the body and 
