ANALYSIS OF BEHAVIOR IN LOWER ORGANISMS 303 



ria, the resumption of the usual forward motion of course carries the 

 organism in a new direction brought about by the reaction. 



What movements are produced by the stimulating agent depends 

 on the action system of the organism; it performs the movements that 

 it is accustomed to perform. In some cases these movements are of a 

 rather uniform character, yet are of such a nature as to subject the ani- 

 mal to many changes of the environmental conditions. This is the case, 

 for example in the reactions of such infusoria as Paramecium. In 

 other cases the movements themselves are varied; the organism first 

 reacts in one way, then in another, running thus through a whole series 

 of activities, till one succeeds in ridding the organism of the stimulating 

 condition. This is the method of behavior seen in Stentor and in most 

 higher organisms. In both methods the essential point is the same 

 — the subjection of the organism to varied environmental conditions, 

 until one of these relieves it from the stimulation. This condition is 

 then said to be "selected." In some cases the maintenance of this 

 favorable environmental condition involves continuance of the move- 

 ment finally resulting from the varied trial movements ; in other cases 

 it does not. 



Reaction by selection of excess movements depends largely on the 

 fact, previously brought out (p. 283), that the movement itself is not 

 directly produced by the stimulus. The movement is due, as we have 

 seen, to the internal energy of the organism. In the case of free-moving 

 animals like Paramecium, stimulation usually neither increases nor de- 

 creases the amount of motion, but merely causes it to change in various 

 ways. Reaction, of course, sometimes does take the form of an increase 

 of motion ; this is seen in the increased movements of infusoria under 

 strong chemicals or heat; of Planaria under light, etc. But even in 

 these cases the energy for the motion comes from within and is merely 

 released by the action of the stimulus. It is important to remember, if 

 the behavior is to be understood, that energy, and often impulse to move- 

 ment, come from within, and that when they are released by the stimu- 

 lus, this is merely what James has called "trigger action." There is 

 thus no reason to expect that upon stimulation an organism will perform 

 merely a single simple movement (a "reflex action"), and then become 

 quiet. Movement of one sort or another is its natural condition, and 

 after stimulation has ceased it may show movements (the character or 

 direction of which may have been determined by the stimulus) for an 

 indefinite period. 



Behavior by selection from the results of varied movements is based 

 on general principles. The reactions are not specific ones, definitely 

 adapted to particular kinds of stimulation, but are responses to any 



