THE INFUSORIA 



179 



factors operating together bring about the spiral course that is 

 pursued in locomotion. There is, however, much more to the 

 behavior than mere forward progression. 



The various responses to stimuli that constitute the beha\ior of 

 paramoecium are effected by modifications of the three factors just 

 mentioned. Thus, if a • paramoecium is swimming forward and 

 comes in contact with a chemical solution that stimulates the cell 



Fig. %. — Reactions of paramoecium. 



A, avoiding reaction. 1-6, successive positions occupied by the animal, not showing 

 the rotation on the long axis. B, path followed by an individual trapped in a drop of 

 acid. C, paramcecium approaching a region containing India ink (shown by the dots). 

 A cone of ink is drawn toward the anterior end and oral groove of the animal. D, para- 

 muecium swinging its anterior end about in a small circle, in a weak avoiding reaction. 

 1, 2, 3, 4, successive positions occupied. (From Jennings, "Behavior of the Lower Organ- 

 isms," reprinted by permission of Columbia University Presa.) 



strongly but does not injure it, the animal responds by reversing 

 its course and may swim backward spirally for a considerable dis- 

 tance before the normal progression is again resumed. The more 

 common reaction, however, is that seen in the responses to less 

 violent stimulation. When, for example, the animal strikes 

 an obstacle (Fig. 96 A), it responds by backing off a short dis- 

 tance, stopping the backward movement, describing a cone 

 by continuing to rotate and swerve dorsally (Fig. 96 D), and 



