CHAPTER VII 

 PROTOZOA 



Habitat. — Protozoa, or one-celled animals, exist in 

 great numbers. They vary greatly in shape, appear- 

 ance and habits. They are found in stagnant water, 

 in fresh water, in the sea, in moist earth, and as para- 

 sites in the bodies of other animals. Malaria is due 

 to one of these forms which becomes parasitic in the 

 bodies of human beings. The common forms may be 

 obtained for study by filling shallow glass dishes with 

 water plants, covering them with water and allowing 

 them to decay. Within two weeks if the water is ex- 

 amined from time to time many different forms will be 

 found. 



The Ameba. — The simplest of these animals is the 

 ameba. It has not even a cell wall. It is nothing but an 

 undifferentiated mass of granular protoplasm contain- 

 ing a nucleus. It moves from place to place, grows, and 

 reproduces, but in the most primitive way. Food is 

 taken in at any point, indigestible materials pass out at 

 any point, and any part of the cell is used for loco- 

 motion. (Figs. 4, 16.) 



The irritability of the protoplasm is responsible for 

 locomotion. The protoplasm flows within the cell and as 

 there is no confining wall the position and shape of the 



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