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 ciha occurs ; with a stronger current 



t the other phenomena 



/ I appear. With a very 



ir%. "f' if j^'^ powerful current, 



^\ %5^ ^1 w y // contraction and dis- 



^vTx \j-^f jf"^ charge of trichocysts 



^«^ '^^^ occur also at the 



I ^^^^""""'l^''''^ I .,^- ^-.'"-" .^^ __ cathode, and with a 



■^ "^^^^NsBs.^— ''^ ^g5N-='=»»si=>-»»»»^ further increase of 



y*^ j!^0\ current, over the 



^^/f /%l%^^\ ^liole body. The 



;^^f y ^H t'l >i.\ animal at the same 



^^^^"^ ^|l |; ^^ time becomes de- 



^\/ formed and usually 



goes to pieces. 



Fig. 60. — Effect of induction shocks on Paramecia in different T tVi t f 



positions. After Statkewitsch (1903). Trichocysts discharged, '-^ tne Current 01 



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



or end, in a. moderate current. ., 1 r -i- 



the reversal of ciua, 

 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 



