82 



BEHAVIOR OF THE LOWER ORGANISMS 



sharply, and trichocysts are thrown out (Fig. 60). If the current is a 

 very weak one, only the reversal of cilia occurs ; with a stronger current 



the other phenomena 

 appear. With a very 

 powerful current, 

 contraction and dis- 

 charge of trichocysts 

 occur also at the 

 cathode, and with a 

 further increase of 

 current, over the 

 whole body. The 

 animal at the same 

 time becomes de- 

 formed and usually 

 goes to pieces. 



In the current of 

 moderate strength 



FIG. 60. Effect of induction shocks on Paramecia in different 

 positions. After Statkewitsch (1903). Trichocysts discharged, 

 cilia reversed, and contraction of the ectosarc, at the anodic side 

 or end, in a moderate current. 



the reversal of cilia, 

 beginning at the anode, quickly spreads over the entire body, causing 

 the animal to swim backward. This movement is the beginning of 

 the avoiding reaction. After swimming backward a short distance the 

 animal turns toward the aboral side and swims forward in a new 

 direction. Thus the reaction to an induction shock is of essentially the 

 same character as the reaction to other strong stimuli. 



Paramecium reacts to induction shocks more readily, as might be 

 expected, when the sensitive anterior end is directed toward the anode. 

 When in this position, it reacts to currents that are too weak to produce 

 reaction in specimens occupying other positions. According to Roesle 

 (1902), Paramecium reacts more readily when the oral surface is toward 

 the anode than when in other positions, indicating that the region about 

 the mouth is especially sensitive. While this seems probable on general 

 principles, it was not confirmed by the thorough work of Statkewitsch 

 (1903). In some cases an induction shock, like a weak mechanical 

 stimulus, causes in place of the avoiding reaction a movement forward 

 (Roesle, 1902). 



Since the animal is most stimulated when the anterior end is directed 

 toward the anode, and this stimulation causes as a rule the avoiding re- 

 action, one would expect that if the stimulation came repeatedly from 

 the same direction, the animal would after a time reach a position with 

 anterior end directed away from the anode. This is exactly what occurs. 

 If frequent induction shocks are passed in a certain direction through 



