CILIARY CURRENT IN PARAMECIA 293 



actually enter them, just as they would if the feeding cone were 

 continuously produced, but not quite so soon. In other words, 

 the reactions in Paramecium, Spirostomum and Stentor are, 

 according to our views, precisely the same in principle, though 

 not quite so efficient as they would be if the feeding cone were 

 continuously produced. However, the contention (Jennings, 

 1904, p. 449) that the spiral course of these organisms is of par- 

 ticular value in testing the condition of the environment in many 

 directions, is questionable. 



SUMMARY 



1. Free-swimming Paramecium, Stentor and Spirostomum do 

 not continuously produce a feeding-cone. Water is sucked toward 

 them from in front through only a very short distance, prob- 

 ably a distance not over twice the length of the cilia. This 

 distance is not great enough to make any warning of unfavor- 

 able environment ahead, which may be due to such currents, of 

 any appreciable value. 



2. The feeding-cone is produced by these organisms : (a) when 

 they are at rest and are feeding; (b) during locomotion if they are 

 retarded by lateral contact with resistant substances which are 

 not uniformly distributed, as e.g. bacterial masses, the substra- 

 tum, etc., or if the rate of locomotion is increasing or if it is 

 decreasing, provided the decrease in rate is due to a reversal 

 or a decrease in the activity of the cilia on the body without a 

 similar change in the activity of those in the oral groove; (c) in 

 the avoiding reaction, but not until after the stimulus which 

 causes such reactions has been received and the animals begin 

 to turn. It is not the cause of the avoiding reaction. 



3. In free-swimming rotifers the feeding-cone appears to be 

 continuously produced. 



LITERATURE CITED 



Jennings, H. S. 1904 The behavior of Paramecium. Additional features and 

 general relations. Jour. Comp. Neur. and Psyc, vol. 14, pp. 441-510. 

 Jennings, H. S. 1906 Behavior of lower organisms. New York, 366 pp. 



