488 Journal of CoDiparative Neurology and Psychology. 



mecia the turning toward the aboral side plays even a larger 

 part than is indicated in the discussion just given. Thus, if the 

 current is frec^uently reversed, the Paramecia practically always 

 become re-oriented by turning toward the aboral side, since 

 after the reversal the anterior end is directed to the anode as in 

 Fig. 14. /-> ; in this position, as we have seen, the turning is al- 

 ways toward the aboral side. It is only l)y taking special pains 

 to close the current when the animal is in such a position as is 

 shown in Fig 14, c that it can be caused to turn toward the 

 oral side. The result is then due to an effect peculiar to the 

 current, which will be taken up later. 



The "action system" in Paramecium further plays a part 

 in the reactions to electricity in the fact that the response on 

 breaking the circuit, and the response to a single induction 

 shock, take the character of the typical "avoiding reaction." 

 This response at the breaking of the circuit is described by 

 Pearl (1900, p. 113); the response to induction shocks by 



SXATKEWITSCH (19O3, p. 48). 



Again, the "acti<:)n system" of Paramecium plays a part 

 in the fact that the path followed during the reaction to the 

 constant current is a spiral of the usual sort, the animal revolv- 

 ing to the left and swerving toward the aboral side. Thus there 

 is during the reaction to the current an obliqueness in the stroke 

 of the cilia similar to that found under usual conditions. Cer- 

 tain variations in the spiral path under the action of the electric 

 current will be taken up later. 



Ptxuliarity of Reaction to the Electric Cnrrcnt. — On the 

 other hand, it is clear that a factor exists in the reaction to the 

 electric current which is not found, so far as known, in the re- 

 actions to other stimuli — a factor not supplied in the "action 

 system" as observed in the movements under the natural con- 

 diti(jns of existence. This is the factor shown in the turning 

 toward the oral side under certain conditions ; the factor that 

 causes the animal to try at times to turn in two opposite direc- 

 tions at once — Pearl's "forced movement factor." What is 

 its nature ? 



The characteristic phenomenon of the reaction to the elec- 



