SAKYO KANDA. 



they tend naturally to orient themselves in the tube with their 

 anterior end toward the axis of the centrifuge as far as their 

 rheotropism is concerned; thus against the current. Therefore, 

 to some extent, this positive rheotropism, when the animal is cen- 

 trifuged, will tend to prevent the downward, i. e., positive "ori- 

 entation" of Paramecium to gravity "at the outset of the 

 centrif ugalization " as by mechanical agitation. In such a case, 

 if the posterior ends of the animals are "heavier' than their 



FIG. i. Tube A ready for centrifuge, and B a part of capillary after centri- 

 fuging, magnified, showing paramecia forced down head first (a slightly modified 

 Lyon's preparation). 



anterior ends, as is supposed by Harper, it would be expected 

 that their posterior ends would be passively thrown to the end 

 of the tube away from the axis of the centrifuge while the anterior- 

 ends would be "oriented" against the water current toward the 

 axis. Thus this method obviates in a measure Harper's criticism 

 rendered on Lyon's experiment. Now the writer put some 

 distilled water in the part be of the tube (see diagram), say about 

 2.5 cm. long, and then added by a small pointed pipette two or 

 three drops of a dense suspension of paramecia, absolutely free 

 from sediment, in the part ab. The tube was fastened to the 

 centrifuge as soon as possible, so that the capillary end when 

 centrifuged should be pointed away from the axis of the machine. 

 After centrifuging at a rate of about fifteen revolutions per second 

 for 10 seconds, the capillary was examined under the low power 

 of the microscope. Every animal was without exception found 

 with its anterior end directed toward the open, outer end of the 

 capillary tube in every trial. This was carefully repeated, 

 varying the speed of the centrifuge, that is, with both higher and 

 lower speeds than 15 revolutions per second. The amount of 

 distilled water in the part be was also varied from a column 

 2.5 cm. long to zero. But this made no difference. 



