Jennings, BeJiavior of Paramecmm. 



491 



rent only the cilia at the cathode tip are reversed (Fig. 16, /). 

 An additional feature, to be observed from the movements of 

 the ciliary currents, is that in the oral groove the cathode effect 

 is more marked than elsewhere, and shows itself by repeated 

 reversals of the ciliary current in the anterior part of this re- 

 gion, lasting but an instant. 



With a stronger current the effective stroke of a part of 

 the cilia of the anterior region of the body is reversed, so as to 

 be forward. At first this includes only a small part of the an- 

 terior region of the body, and this result is reached first in the 



oral groove, where a water current 

 passes continually forward even 

 when the electric current is so weak 

 that over the remainder of the an- 

 terior part of the body the water 

 currents are still backward or at 

 rest (Fig. 15, a). As the electric 

 current is made stronger, the cur- 

 rents pass forward over the entire 

 anterior half of the body. This is 

 the stage usually considered typi- 

 cal, though as Statkewitsch (1903 

 a, p. 93) points out, it is only one 

 point in a series of continuous 



Fig. lb. Different stages of the reaction of the cilia to the electric cur- 

 rent, after Statkewitsch (1903 a). The cathode is conceived to be above, the 

 anode below. In a weak current, only a few cilia at the tip of the cathode end 

 are reversed (i). As the current becomes stronger (2, 3, 4, 5, 6) more and more 

 of the cilia are reversed, until in the strongest currents practically all of the cilia 

 strike forward. 



changes. At tliis stage there is still an alternation at intervals 

 in the direction of the effective beat of the cilia of the anterior half 

 of the body, giving the movement a jerky character. As the 

 electric current is made stronger the forward water currents on 

 the anterior half of the body become constant and more pow- 

 erful; the currents on posterior and anterior halves separate at 

 about the middle of the body, and water is drawn from all sides 



