Jennings, Behavior of Parauuxmin. 449 



of the water in front of it, and reacting to these samples. In 

 its spiral path Paramecium becomes pointed successively in 

 many different directions, so that it "samples" the water from 

 many directions (Fig. 3). When the spiral is very narrow, the 

 animal swimming rapidly forward, these samples all come from 

 near the axis of the spiral and therefore show little variation. 

 But in most cases the direction from which they come is contin- 

 ually changing. Thus we may say that Paramecium, through 

 its spiral course, is continually "trying" the water in various 

 directions. Or, to express the same thing in a more objective 

 way, through the spiral course the most sensitive portion of 

 the organism is subjected successively to water coming from 

 many different regions. 



In another way the spiral course subjects the organism to 

 varied experiences. Suppose that a force which acts in straight 

 lines from a definite direction is operating on the swimming organ- 

 ism from one side ; for example, light, or the electric current, 

 or gravity, or a current of water. By its spiral course the or- 

 ganism is brought successively into different relations with this 

 agent (Fig. 3). In one phase of the spiral, as at d, it swings 

 more nearly into paralellism with the lines of action of the agent ; 

 in another it is becoming more nearly transverse, as at h. In 

 the case of light the anterior end is becoming more illuminated 

 in one phase, less in another ; in other words, the anterior end 

 is subjected to continual variations in the intensity of illumina- 

 tion. With gravity, or a water current, the swinging is assisted 

 in one phase of the spiral, resisted in another, so that the ani- 

 mal is subjected to continual variations in the resistance it meets. 

 These changes give opportunity for directive or regulative stim- 

 ulation. It is only when the axis of the spiral course is in the 

 lines of force — in other words, when the organism is "orient- 

 ed" — that such changes cease. These relations will be brought 

 out in detail later in describing the reactions to certain stimuli. 



Altogether, we see that the "action system" of Parame- 

 cium contains elements of such a nature as to subject the animal 

 to the greatest possible number of changes in the environment, 

 thus giving it opportunity to react to all such changes. 



