492 Journal of Comparative Neurology and Psychology. 



to supply them, making the animal the center of a sort of 

 cyclonic disturbance in the water (Fig. 15, /;), which gives a 

 most extraordinary appearance. At this stage the forward 

 movement of the animal is much retarded, owing to the strong 

 backward stroke of the cilia on the anterior half of the body. 



With a still stronger electric current the forward ciliary 

 currents in the anterior (cathodic) region of the body become 

 still more powerful and extensive, seeming to begin even be- 

 hind the middle, though the precise boundaries of the two sets 

 of currents are very difficult to determine by this method of ob- 

 servation. There comes a period when the effect of the two 

 sets of currents are equal, and the animal neither advances nor 

 retreats, but retains its position, revolving rapidly on the long 

 axis. It is clear that the forward stroke of the anterior cilia 

 just balances the backward stoke of the posterior cilia. Often 

 the two sets of cilia alternate in obtaining the upper hand ; the 

 animal is driven backward a distance, then forward again. If 

 the electric current is made still more powerful, the forward 

 currents in front become still stronger and more extensive ; they 

 gain the upper hand permanently, and the animals are driven 

 backward toward the anode. 



For stronger electric currents it is not possible to determ- 

 ine by observation of the ciliary currents the distribution of for- 

 ward and backward striking cilia. But this has been determined 

 from direct observation by Statkewitsch (1903, a); his re- 

 sults are shown in Fig. 16. The reversal of the cilia, begin- 

 ning with a weak electric current at the cathodic tip, extends 

 backward as the current becomes stronger till it finally includes 

 practically the entire body surface. 



In view of these results, the known facts as to the reaction 

 to the electric current may be formulated at follows. First, the 

 current stimulates in the same manner as any other stimulus ; 

 this stimulation has origin at the anode. Second, the results 

 of this stimulation are interfered with or overcome by an effect 

 peculiar to the electric current, and having origin at the cathode. 

 This peculiar effect is shown in a progressive reversal of the 

 cilia, beginning with a weak current at the cathode tip, and 



