THE SIMPLEST ANIMALS OR PROTOZOA 



23 



23. The Amoeba. Among the simplest one-celled ani- 

 mals living in the ooze at the bottom of nearly every fresh- 

 water stream or pond is the Amoeba (Fig. 7, A), whose body 

 is barely visible to the unaided eye. Under the microscope 



Fio. 7. A, the Amoeba, highly magnified, showing c. v,, pulsating vacnole ; /, food 

 particle ; n, nucleus. The arrows show the direction of movement. B, shape of 

 same individual 30 seconds later. C, an amceba-like animal (Difflugia) partially 

 enclosed in a shell. D, an Amoeba 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. TJnlike 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 projections at the opposite end of the cell are withdrawn, 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 



