192 



THE BEHAVIOR OF LOWER ORGANISMS. 



turned and began to move toward the cathode {b) , dragging the parti- 

 cles of soot behind it for a short distance. Then the string of soot began 

 to pass forward on the upper surface, in the usual way (c, d) . This 

 continued until the soot reached the anterior edge and dropped off the 

 surface of the Amoeba {e). The currents on the upper surface of Amoeba 

 are, then, forward (toward the cathode) in the reaction to the electric 

 current, as well as in other cases. 



On reversing the current the specimen described above began to 

 move in the opposite direction toward the new cathode. In this and 

 many other observed cases of the reversal of movement under the in- 

 fluence of the electric current, the reversal occurred in the same manner 

 as when induced by other stimuli (see p. 183). That is, the new pseudo- 

 podium was sent out from one side of the attached (anterior) half of the 

 body, changing the course a certain amount. From this new portion 

 another new pseudopodium was sent out on the side toward the anode, 



.'X 



Fig. 72.* 



and this continued until the direction of movement had been, by a 

 gradual process, completely reversed. Vei'worn (/. c.) describes cases 

 in which the reversal takes place suddenly, the new pseudopodium 

 appearing at the original posterior end. This happens also at times, as 

 we have seen, in the reactions to other stimuli (p. 1S3). It is to be noted 

 that the reaction to the electric current is exactly that which would 

 occur if the animal were sti'ongly stimulated on the anode side. 



Verworn (18S9), Davenport (1S97), and Harrington & Leaming 

 (1900) have studied the reaction of Amoeba to light. Verworn (/. c, 

 p. 97) found that light falling perpendicularly on one-half of the Amoeba 

 produced no reaction. Davenport (/. c, pp. 1S6, 188) confirmed this 

 result, but showed that when the light falls obliquely from one side on 

 Amoeba the animal reacts negatively. Harrington & Leaming (/. c.) 

 found that when white light falls upon the Amoeba from above the 



*FiG. 72. — Movement of particles attached to the outer surface of Amceba in 

 the reaction to the electric current. Anode and cathode are represented by the 

 plus f-f-) and minus ( — ) signs, a, Form and direction of movement of the Amceba 

 before the current is made ; x, a chain of soot particles attached to one side ; b, c, 

 d, e, successive stages during the reaction. The chain of soot particles (x) passes 

 to the upper surface and forward, reaching at e the anterior edge. 



