498 Journal of Comparative Neurology and Psychology. 



of the particles of India ink, is now everywhere backward, save 

 in the oral groove, where it is usually forward though at inter- 

 vals it here passes backward for a moment. 



If while in this position the direction of the current is re- 

 versed, so that the oral surface is toward the anode, the oral 

 cilia strike .strongly backward. This has one of two effects. 

 Sometimes it causes the animal to be detached from the surface ; 

 in this case it turns toward the aboral side until the anterior end 

 is directed to the cathode, then it swims forward in that direc- 

 tion, like other free swimming specimens Or the animal may still 

 remain in contact with the surface ; in this case it turns toward 

 the aboral side, until the peristome or oral surface is again di- 

 rected toward the cathode. Then it remains quiet, or resumes 

 its forward movement transverse to the current In cultures 

 where the specimens are much inclined to be thii^niotactic, one 

 often observes in this way marked transverse elcctrotaxis in a 

 large number of individuals ; by repeatedly reversing the cur- 

 rent the\- can be driven from one side of the preparation to the 

 other and back again, always transversely or obliquely to the 

 current. 



RoE-SLE (1902) observed that Par.imecium reacts much 

 more readily to induction shocks when the peristome is directed 

 toward the anode than in other positions. Roesle interprets 

 this as showing that the peristome is more sensitive than other 

 parts of the body surface. While this conclusion is a priori 

 very probable, I am not sure that the facts cited really demon- 

 strate it. When the constant current is made, the anitnal lying 

 against a surface with peristome to the cathode, there is a reac- 

 tion, which is, however, ineffective in causing a movement of 

 the animal's body. The reaction consists in a weak reversal of 

 stroke of the oral ciHa, as is shown by the forward movement 

 of the particles of Int'ia ink in the oral groove. This forward 

 stroke of the oral cilia has very little locomotor effect, 

 and does not overcome the attachment of the animal to 

 the surface ; it could not be observed without the presence of 

 the particles of India ink. It is possible that this reaction oc- 

 curs also with mduction shocks, and escaped observation, owing 



