STIMULI AND THEIR ACTIONS 457 



If the current be broken, the assemblage disappears from the 

 kathode, and the Paramcecia scatter themselves again uniformly 

 throughout the liquid. If the Paramcecia be put into a large 

 drop upon a glass plate, and the pointed electrodes be dipped 

 into the drop, upon making the current the infusorians arrange 

 themselves in the direction of the curved lines of flow of the 

 current like iron filings above a magnet, and swim in this direction 

 (Fig. 231) until they have reached the kathode, behind which they 

 collect in a dense swarm. If the kathodic electrode be made 

 movable, so that its position in the drop can be changed at will, it 

 is possible to direct the Paramcecia with the point of the electrode 

 wherever one wishes, just as tin-fishes may be directed in water 



FIG. 231. Galvanotactic curves of swimming Paramcecia, pointed electrodes being used in the 

 drop of water. A, Beginning of the effect; B, completed assemblage. 



with a magnet. Since the motion of the Paramcecia is directed 

 toward the kathode, this case may be termed kathodic galvanotaxis. 



Like Paramcecium, the majority of the ciliate Infusoria are 

 kathodically galvanotactic. Among other Protista that show 

 the same phenomenon, Amoeba alone may be mentioned. Amoeba 

 Umax, when the current is made, abandons its original direction ; 

 its pseudopodia flow forward toward the kathode, the whole proto- 

 plasmic mass streams after, and the body assumes the typical 

 extended creeping form, in which it flows unerringly to the kathode. 

 Other forms of Amoeba, such as Amoeba proteus (Fig. 232), Amoeba 

 verrucosa, and Amoeba diffluens (Fig. 233), behave in all respects 

 similarly. 



Many flagellate Infusoria show a behaviour opposite to that of 

 the above-mentioned organisms. If, e.g., a constant current be 

 passed through a drop in which is a large number of individuals of 

 the small egg-shaped species, Polytoma uvella t which move through 

 the water, revolving continually about their axis, by means of their 

 two flagella (Fig. 234), upon making the current all individuals 

 immediately turn their anterior flagellated ends toward the anode, 

 and freely swim in their usual manner straight to this pole, where 



