THE GEOTROPISM OF PARAMECIUM CAUDATUM. 113 



count of its heavier weight, was originally demonstrated by Lyon. 

 This was the strongest in his experiments to cast aside the 

 "mechanical theory." The writer supported him by furnishing 

 results obtained by improved methods to meet Harper's criti- 

 cism. 1 Harper insisted that in strong centrifugalization, "the 

 same effect is produced at the outset as by mechanical agitation, 

 i. e., the reaction changes to positive." In other words Harper 

 claims that the head is turned outward by a positive response on 

 the part of the organism, and not passively, as claimed by Lyon. 

 The writer showed in his previous paper that Harper could not 

 be right. 



However, McClendon thinks that "the geotropic reaction" 

 of the animal "may be strong enough to turn the anterior end in 

 the opposite direction" toward the axis of the centrifuge against 

 the centrifugal force. This needs a serious examination. If the 

 anterior end of the animal is considered "heavier" than the 

 posterior, as Lyon and Kanda hold, it is hardly conceivable that 

 such a small animal as Paramecium could orient itself with the 

 heavier end toward the axis of the centrifuge against the force 

 McClendon used. On the other hand, if the posterior end is 

 regarded "heavier" than the anterior, as Verworn 2 and Harper 

 hold, one meets the same difficulty to conceive how the animal 

 can orient itself with the "lighter" anterior end away from the 

 axis of the centrifuge against the much greater force used by 

 Lyon and the writer. McClendon admits that "this is usually 

 the initial orientation," but seems to' think the animals may occa- 

 sionally turn around later by an active reaction. The writer 

 must confess that he cannot conceive its possibility. He found 

 one individual among several dozen examined which was thrown 

 with the posterior end away from the axis of the centrifuge. He 

 considers, however, that this was a mere accident, the animal 

 being oriented in that direction at the beginning of centrifugali- 

 zation and forced into the capillary before passive turning could 

 occur. McClendon's case was also probably exceptional and 

 moreover had been centrifuged twenty-four hours, during which 



1 Harper, E. H., 1911, "The Geotropism of Paramecium," Jour. Morph., Vol. 

 22, p. 998. 



2 Verworn, Max, 1889, " Psycho-Physiol. Protisten-Studien," Jena: Gustav 

 Fischer, p. 121. 



