CILIARY CURRENT IN PARAMECIA 



289 



the edge of the cloud. At no time during the reaction or before 

 is the ink drawn out in the form of a cone. This fact strongly 

 supports our contention that the cone is not continuously pro- 

 duced in free-swimming paramecia. 



A few observations seem to indicate that in the weak avoiding 

 reaction the animals continue to turn as long as the current pro- 

 duced in the feeding cone carries stimulating substance to the 

 oral groove. Usually the weak avoiding reaction occupies but 



Figs. 4 and 5 A Paramecium responding with a weak avoiding reaction after 

 coming in contact with acidified ink. 1', 2', 3', 4', successive positions of the 

 Paramecium; 2, 3, 4, corresponding positions of the feeding cone. Note that the 

 feeding-cone is not produced until after the anterior end has come in actual con- 

 tact with the ink and that the Paramecium stops turni.:g as soon as the ink no 

 longer comes in contact with it. 



the briefest interval. The paramecia swim up to the edge of a 

 cloud of ink, turn rapidly to one side and swim away, leaving a 

 streamer of ink at the edge of the cloud, all so quickly that the 

 details of the process can not be observed. Occasionally, how- 

 ever, the reaction takes place more slowly and in some such 

 cases it seems that the aboral rotation persists just so long as 

 the current of acidified ink comes in contact with the oral groove, 

 and that the backward stroke of the body cilia is resumed as 

 soon as stimulation of the oral groove ceases. 



Two such reactions are represented in figures 4 and 5. Both 

 were observed when the majority of the paramecia in the prepa- 



