FACTS AND FACTORS OF DEVELOPMENT 



67 



But although limited in its behavior to these 

 relatively simple motor reactions, Paramecium 

 does many things which seem to show intelli- 

 gence and purpose. It avoids many injurious 

 substances, such as strong salts or acids, and it 

 collects in non-injurious or beneficial sub- 

 stances, such as weak acids, masses of bacteria 

 upon which it feeds, etc. It avoids extremes 

 of heat and cold and if one end of a dish con- 

 taining Paramecia is heated and the other end 

 is cooled by ice, the Paramecia collect in the 

 region somewhere between these two extremes 

 (Fig. 17). Jennings, by studying carefully 



Fig. 21. Diagram of the Avoiding Reaction of Parame- 

 cium. A is a solid object or other source of stimulation. 1-6, 

 successive positions occupied by the animal. The rotation on 

 the long axis is not shown. (After Jennings.) 



