686 



RAYMOND PEARL. 



the body is approximately at riglit angles to the direction of 

 the cnrrent, niny be described first. If a number of speci- 

 mens are g-liding- about at the normal rate, and a current of 

 from Aveak to medium intensity is made through the prepara- 

 tion, the first reaction of all the specimens is to stop their 

 forward motion, turn towards the kathode, and start crawling 

 very slowly towards this pole. The orientation towards the 

 kathode is at the first trial usually rather precise. The whole 

 animal gets squarely into line with the current and moves 

 slowly towards this pole. While the current is acting the 

 anode end of the body, in this case the posterior end, remains 



+ - 



3 + 



d 



Pjg. 42. — Diagram showing; I lie typical electiofaclic reaction of PI an aria. 

 a. Position at the moment of making the current, b, c, and d. Suc- 

 cessive phases of the reaction. 



rather strongly contracted, presenting the same appearance 

 as when mechanically stimulated. Movement occurs only for 

 a short time after the current begins acting. The worm soon 

 comes to rest, and further stimulation serves only to cause 

 contraction of various parts of the body without producing 

 any progressive movement. The successive stages of the first 

 typical reaction to the constant current are shown in Fig. 42. 

 In succeeding experiments on a given individual, and in 

 many cases with the very first experiment, the reaction is 



