Jennings, Bchavioj' of Paraviecinni. 483 



C. Responses to Stivmli not brought about thro2ig]i tJie "Avoid- 

 ing Reaction. 



The behavior which we have thus far considered is brought 

 about chiefly through the avoiding reaction ; the general method 

 is that of "trial and error. " Though the most important fea- 

 tures of the behavior of Paramecium are produced in this way, 

 there are certain other reactions in which the method of "trial 

 and error" does not play the chief, or at least the only part ; 

 in these the relation of the direction of movement to the source 

 of stimulus is, in certain features at least, more direct. These 

 reactions we shall take up next, though only with the reaction 

 to the electric current shall we deal here in detail. A list of 

 these reactions was given on page 450. Local contraction of 

 the body as a response to stimulation has been dealt with suffi- 

 ciently above (page 457), and in the paper of Statkewitsch 

 (1903). Massakt (1901) gives a thorougli study of the dis- 

 charge of trichocysts as a response to various stimuli, while 

 Statkewitsch (1903) gives details as to the production of this 

 reaction by induction shocks. The reaction to contact by com- 

 ing to rest has been described in detail in a previous paper by 

 the present author (Jennings, 1897), and in a more recent pa- 

 per by Putter (1900). These matters, then, we need not con- 

 sider further here. 



I. Forward Movement as a Response to Stimulation. 



In a previous paper (Jennings, 1900) I showed that many 

 Infusoria respond to a stimulus which affects only some other part 

 of the body than the anterior end, by moving forward. I did 

 not succeed in showing this for Paramecium, owing to diffi- 

 culties of technique in working with so small an animal. In 

 the meantime Roesle (1902) has observed that when a speci- 

 men is stimulated at about the middle of the body by col- 

 lision with another specimen, it responds by moving forward. I 

 have recently been able to confirm this result experimentally. 

 A small glass rod may be drawn out so fine that the tip is hard- 

 ly visible under a magnification such that the differentiations in 

 the body of Paramecium are conspicuous and cilia are plainly 



