REACTIONS OF OPALINA RANARUM 333 



4. Mechanical stimuli sometimes induce the avoiding reac- 

 tion. Opalina frequently swims indifferently up to glass, needle, 

 filter paper and other objects, remaining against them as if in 

 contact with food. Opalina responds by retreating when the 

 anterior end is touched with a fine rod but does not react when 

 the side of the body is stimulated. 



5. Opalina lives in both acid and alkaline media. When in 

 an alkaline medium it reacts positively to acids and negatively 

 when encountering neutral and basic salts. It may cease to 

 react to a chemical after repeated stimulation and remain in 

 the chemical. Solutions of different strengths cause the avoid- 

 ing reaction when Opalina swims from one to the other. Opalina 

 does not avoid strong acids. 



6. Opaiina does not react to heat or cold. It is much more 

 resistant to cold than to heat. It may live at temperatures 

 of from 2° C. to 22° C. 



7. Light apparently has no effect on the orientation or move- 

 ment of Opalina. 



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1907 Science, 51, 633-646. 

 Jennings, H. S. Studies on reactions to stimuli in unicellular organisms. I. Re- 

 1897 actions to chemical, osmotic and mechanical stimuli in the ciliate 



infusoria. Journ. of Physiol., 21, 258-322. 

 1900 Studies on reactions to stimuli in unicellular organisms. II. On the 

 movements and reactions of the Flagellata and Ciliata. Amer. Journ. 

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 1906 Behavior of Lower Organisms. New York. 366 pp. 



Kunstler, J. et Gineste, C. Orientation du corps des Opalines. C. R. Soc. 



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