i6o 



BEHAVIOR OF THE LOWER ORGANISMS 



of the convexity of the right side (Fig. 107, x) are very easily reversed 

 by a weak current. The cilia of the opposite side, on the other hand, 

 are little affected by a weak current. Their usual backward stroke is 

 decreased in power, and doubtless some of the cilia are reversed, but the 

 general effect of their action is still to drive the animal forward. Let 

 us suppose that the Opalina is at first transverse to the electric current, 

 with right side to the cathode, as in Fig. 107, 1. As soon as the current 



Fig. 107. — Diagrams of the movements of the cilia, and of the direction of turning, in the 

 reaction of Opalina to the electric current. After Wallengren (1902). 



begins to act, the cilia of the right (cathodic) side become directed for- 

 ward, while those of the left (anodic) side remain directed backward. 

 The result is of course to turn the animal to the right, toward the cath- 

 ode. Thus the specimen passes through the position shown in Fig. 

 107, 2, and comes into a position with the anterior end directed toward 

 the cathode (3). The cilia of the anterior part of the body are now 

 directed partly forward, those of the posterior half backward. In this 

 position, as we know, Paramecium remains ; indeed, the whole reaction 

 thus far is essentially like that of Paramecium. But in Opalina, so long 



