4 SAKYO KANDA. 



strongly are passively thrown to the bottom of the tube." "A 

 glass tube was drawn into a capillary so fine that paramecia 

 could not turn around in it. The capillary end was dipped into 

 distilled water and the tube filled by capillarity . . . ; then the 

 end was sealed and a drop of w r ater containing paramecia was 

 introduced into the large part of the tube. The tube was fastened 

 to the centrifuge so that the capillary pointed away from the 

 axis of the machine. After strong rotation the capillary was 

 examined under the microscope. The organisms were invariably 

 found w T ith anterior ends directed towards the closed end of the 

 tube." From these results, Lyon concludes: "It is therefore 

 certain that passive paramecia would fall head end down, and 

 that their negative geotropism is the result of an active process 

 on the part of the animals. Jensen's view in this respect is fully 

 confirmed and the mechanical theory is to be laid entirely aside" 

 (17, p. 423). 



Judging from Lyon's results, the anterior end seems to be 

 "heavier" in spite of the larger shape of the posterior end. Thus 

 Verworn's theory as well as Davenport's supposition of a static 

 equilibrium (2, p. 122) are found untenable. 



Very recently, however, Harper has taken up the problem and 

 in his two articles has again revived the "mechanical theory' 

 (3-4). He adopted the method of Kreidl (13) and that of 

 Prentiss (21) who made crustaceans take in iron-filings as 

 "statoliths" and then applied a magnet. Harper made Para- 

 mecium caudatnm ingest finely divided iron prepared by the 

 alcohol method. In so doing he varied the time for the ingestion 

 of iron, from 30 40 seconds to five minutes. He seems to have 

 obtained his best results when the ingestion of iron w r as allowed 

 to continue for one minute. 'The treated animals," he says in 

 his first article, "swarmed to the top more quickly and formed a 

 denser ring there than in the control" (p. 996). From this 

 result and others, Harper drew th'e conclusion that "the pull of 

 gravity on the heavier posterior end may produce a tipping effect 

 which is able to orient passively but is too weak to stimulate." 1 

 And he believes that here "we have in the normal, quiet, geo- 

 tropic reactions of Paramecium an example of a purely mechanical 

 tropism" 1 (3, p. 998). 



1 All italics not in the original. 



