486 Journal of Coniparative Neurology and Psychology. 



aboral ones, they turn the organism toward the aboral side. 

 But this is aided by the fact that the ciha of the aboral side of 

 the anterior half of the body strike obliquely toward the oral 

 side. So far then as the anterior half of the body is concerned, 

 this reaction is the same as that produced by other stimuli. In 

 the posterior half, directed toward the cathode, another factor 

 plays a part, to be taken up later ; but this has under the pres- 

 ent conditions no effect on the reaction. 



e 



fig. j^. Diagram representing the action of the cilia and the direction of 

 turning in Paramecia occupying different positions with relation to the electric 

 current. The small arrows within the outlines of the body represent the direc- 

 tion in which the cilia of the different regions tend to turn the animal ; the 

 larger external arrows represent the actual direction of turning. In all positions 

 from a io J the turning is toward the aboral side ; at ^ it is toward the oral side. 



Even when the animal lies in a very slightly oblique position, 

 so that orientation would be reached somewhat more quickly 

 by turning toward the oral side (Fig. 14, a), the turning is 

 still toward the aboral side, the strong oral cilia striking back- 

 ward and driving the animal toward the aboral side. Further, 

 when the animal is transverse to the current and the aboral side 

 is toward the cathode (Fig. 14, c), the turning is of course to- 

 ward the aboral side, as inspection of the figure shows it must 



