Jennings, BcJiavior of Parmncchim. 497 



order to show the interference described. It occurs also when 

 the animals are in contact with a clean glass surface, or the 

 surface film of water. This is particularly evident when the 

 Paramecia are subjected to a moderately strong current on the 

 slide in a thin layer of water, without a cover. They swim as 

 usual toward the cathode. But when a specimen in its spiral 

 course comes against the glass slide or the surface film, it at 

 once stops. It may stop only an instant, or it may remain at 

 rest for some time ; or it may show certain peculiar movements, 

 to be described later. 



2. The effect of thigmotaxis appears not merely in a de- 

 crease in sensitiveness to to the current, but in a change in the 

 method of reaction to the current. Putter (1900) showed that 

 in various Hypotricha individuals in contact with a surface take, 

 in the current, a nearly transverse position with the left side 

 (bearing the peristome) to the cathode, while free swimming in- 

 dividuals become oriented with anterior end to the cathode. 



Similar relations are to be obser- 

 ved in Paramecium, though less 

 frequently than in the Hypotri- 

 cha, because Paramecium is less 

 often in contact with the surface. 

 But when a large number of 

 individuals are subjected to the 

 current in a thin layer of water 

 (with or without a cover glass), 

 the phenomena are evident. 

 The free specimens swim as 

 usual, with anterior ends to the 

 cathode. Those that come in contact with the surface film or 

 the glass, stop, as described above. If they do not quickly re- 

 sume the forward course, they soon take up a position nearly 

 transverse to the current, with the oral side or peristome direct- 

 ed toward the cathode (Fig. 17). In this position they may 

 either remain quiet, or may move forward transversely (or ob- 

 liquely) to the current, keeping in contact with the surface. 

 The effective beat of the cilia, as determined by the movements 



+ 



f^*S- n- Transverse or oblique 

 orientation of Paramecium to the 

 electric current when in contact with 

 a surface. 



