XII 



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7 V 



. . turning point of Paramecium. 

 . . whirling point of Paramecium. 

 . . turning point of Oxytricha. 

 . . course of Vorticella. 



The above figure shows both the arrangement 

 of the experiment and an example of these differen- 

 ces. The circle in the middle represents a dried up 

 drop on the slide, containing plenty of dead Para- 

 mecia. Next to this drop are placed those other drops 

 which contain the different species of infusoria whose 

 irritability in face of the dead bodies is to be ex- 

 amined. They must be placed so as to cover a small 

 part of the dried drop. The black points mark the 



