PROTOZOA 87 



There is no trace of a nervous system, though the animal 

 displays many of the reactions to stimuli which higher forms 

 possess. It is sensitive to chemical changes in the water sur- 

 rounding it and to heat, moving away from the chemically 

 changed area and from the source of heat. It moves away 

 likewise from the source of strong light and toward the negative 

 pole when the water containing it is charged with electricity. 

 It avoids mechanical obstacles in the water by reversing the 

 flow of its protoplasm into the opposite direction. Thus me- 

 chanical, chemical and electrical stimuli and variations in heat 

 and light control the direction of movement (15). 



Reproduction is mainly by simple division. When more 

 food is taken in than is required for maintaining the size un- 

 altered, a constriction appears dividing the entire amoeba, 

 including the nucleus, into two parts, thus producing two 

 cells or two individuals. Each individual amoeba is a single 

 cell, that is, it consists of a mass of protoplasm with an included 

 nucleus. All animals higher than Protozoa, as well as all higher 

 plants, consist of many such cells, usually with some more or 

 less firm protective or strengthening substance. 



1. If Amoeba is available it should be examined under a 

 compound microscope, its shape and movements noted. 



2. Give size and structure of the animal. Illustrate with 

 sketch. 



3. Where does it Hve ? What does it feed upon? 



4. How is food procured ? How digested, and waste thrown 

 off? 



5. How is the food assimilated ? 



6. How does the animal breathe ? Excrete waste matter ? 



7. Does Amoeba possess nerves ? How does it respond to 

 stimuh ? 



8. Describe its reproduction. 



9. Where do Protozoa occur? What is meant by calling 

 them one-celled animals ? 



10. What classes of Protozoa have been found fossil ? 



