84 



BEHAVIOR OF THE LOWER ORGANISMS 



duced by the cilia becomes evident.' In this way we find that it is not 

 alone at the anode that the electric current is active, but that a peculiar 

 effect is produced also at the cathode. Here the direction of the cilia 

 is reversed (Fig. 61) so that they point forward, and their effective stroke 

 is forward, tending to drive the animal backward. When the electric 



current is weak and the animals are swim- 

 ming toward the cathode, the ciha are re- 

 versed only at the anterior end (Fig. 61, i), 

 the reversal extending a little farther down 

 on the oral side than elsewhere. At the 

 anterior tip the water currents are forward 

 instead of backward (Fig. 62, a), and the 

 cilia themselves are clearly seen to be 

 pointed forward (Fig. 61, i). When the 

 animal is swimming most rapidly toward the 

 cathode, this effect is very sUght; almost 

 all the cilia of the body are beating back- 

 ward in the usual way. 



If the current is made stronger, this 

 cathodic effect increases. The ciha become 

 Fig. 61. — Progressive cathodic reversed farther and farther back, till with a • 



reversal of the cilia and change of , . , ^i r ^i i i • ^ ii. 



form in Paramecium as the con- Certain Strength of the elcctnc Current the 

 stant electric current is made cilia on the anterior half of the body are 



stronger. The cathode is supposed , -i ■ r j ii ii i. • i. ir 



to lie at the upper end. The cur- Striking forward, those on the posterior half 



rent is weakest at i, where only a backward (Fig. 6l, 3).^ The water CUr- 

 few cilia are reversed. 2-6, Sue- . . 1 . ,,-,,,. 



cessive changes as the current is ^cnts produced are in Opposite directions, 

 gradually increased. After Statke- making the animal the Centre of a sort of 

 wi sc 1903 a . cyclonic disturbance in the water, which 



gives a most extraordinary appearance (Fig. 62, b). The two sets of 

 ciha oppose each other, so that the animal seefis to be trying to swim 

 in two opposite directions at once. Up to a certain strength of the elec- 

 tric current the posterior cilia prevail over the anterior ones, so that the 

 animal swims forward. But the movement becomes slower and more 

 labored as the electric current is increased, until in time the two sets of 

 cilia balance each other. Then the animal remains in place, revolving 

 rapidly on its long axis, or it shoots first a short distance forward, then 

 a little backward. With a still further increase of the electric current, 

 the cathodic effect increases to such an extent that the reversed cilia gain 



' The Paranaecia must be in a thin layer of fluid; this may be attained by supporting 

 the cover-glass on thin sheets of filter paper and introducing the current through this 

 paper. 



' This peculiar eSect v>ras first observed by LudloEE (1895). 



