1 62 BEHAVIOR OF THE LOWER ORGANISMS 



made stronger. But as the current is increased, the forward stroke of 

 the cilia on the left side of the anterior half of the body becomes more 

 powerful, — just as happens with all the anterior cilia in Paramecium. 

 Hence, when the current reaches a certain strength, the cilia of the left 

 side, in an Opalina pointing toward the cathode, beat as strongly for- 

 ward as do those of the right side. There is then no cause for turning 

 toward either the right or the left. The position with anterior end 

 directed toward the cathode has become a stable one. Thus, when a 

 strong current is passed through a preparation of Opalinas, most of them 

 become directed after a time toward the cathode, and swim slowly in that 

 direction. A number may be at first directed toward the anode, but as 

 soon as these by any chance get out of the anode-pointing position, they 

 also become directed toward the cathode. 



With a still more powerful current the Opalinas retain nearly or 

 quite the position with anterior end to the cathode, but move backward 

 (or sometimes sideways) toward the anode. Wallengren believes that 

 this is a passive movement due to the cataphoric action of the electric 

 current. In Paramecium, as we have seen, there is a similar move- 

 ment under these conditions, but due to the fact that the cathodic cilia 

 beat more effectively forward than do the anodic cilia backward. 



Thus altogether we find that in Opalina the electric current acts on 

 the motor organs in fundamentally the same way as in Paramecium. 

 But owing to peculiarities of the action system of Opalina, this results, 

 with a weak current, in movement forward toward the anode; with a 

 stronger current in movement forward toward the cathode; with a still 

 stronger current in movement backward or sideways toward the anode. 



2. Summary 



Reviewing our results as to the effect of the continuous electric cur- 

 rent on the ciliate infusoria, we find a complete agreement throughout 

 in the action of the current on the motor organs, with the greatest pos- 

 sible diversity in the resulting movements of the animals. In all cases 

 the cilia in the anode region strike backward, as in the normal forward 

 movement, while the cilia of the cathode region are reversed, striking 

 forward. With different strengths of current, and with infusoria of 

 different action systems, this results sometimes in movement forward to 

 the cathode ; sometimes in movement forward to the anode ; sometimes 

 in a cessation of movement, the anterior end continuing to point to the 

 cathode ; sometimes in a backward movement to the anode ; sometimes 

 in a position transverse to the current, the animal either remaining at 

 rest or moving across the current. These variations depend upon the 



