86 



BEHAVIOR OF THE LOWER ORGANISMS 



the backward stroke of the oral cilia is more powerful than that of the 

 opposing aboral cilia. For the same reason the animal turns toward 

 the aboral side even when in the position shown in Fig. 63, a, where it 

 would be more direct to turn toward the oral side. Between this posi- 

 tion (a) and the transverse position with oral side to the cathode (e), 

 there is a position in which the tendencies to turn in opposite directions 

 are exactly balanced (/). The animal tries, as it were, to turn in opposite 

 directions at the same time, so that it remains in position, though the 



(/- 



Fig. 63. — Effects of the electric current on the cilia of Paramecia, and direction of turning 

 in different positions. The oral side is marked by an oblique line. The large arrows show 

 the direction toward which the animal turns. The small internal arrows indicate the direction 

 in which the cilia of the corresponding quarter of the body tend to turn the animal. In all 

 positions save c and e the cilia of different regions oppose each other. From a to d the turning 

 is toward the aboral side; from d to /, toward the oral side. At / the impulse to turn is equal in 

 both directions, and there is no result till by revolution on the long axis the animal comes into 

 a position with aboral side to the cathode. 



cilia are beating violently, causing complicated currents in the water. 

 This independent and opposing activity of the cilia of different parts of 

 the body is characteristic of the effects of the electric current, and is not 

 found in the reactions to other stimuli. In the position shown in Fig. 

 63, /, the revolution on the long axis, which is a part of the normal 

 motion of the animal, soon interchanges the position of oral and aboral 

 sides, whereupon the infusorian of course turns at once towards the 

 aboral side, till its anterior end is directed toward the cathode. 



Thus in a considerable preponderance of all possible cases the ani- 



