24 BEHAVIOR OF THE LOWER ORGANISMS 



of locomotive power. Would it give a more adaptive reaction than 

 Amoeba? Evidently, the conditions are such that it is impossible for 

 the animal to escape by any means from the current. Since the stimu- 

 lation apparently comes most strongly from the anode side, it is natural 

 to move in the opposite direction. The method of the negative reaction 

 is that of a trial of certain directions of movement. This method is in 

 essence an adaptive one, and if it fails in the present case, certainly no 

 better course of action can be suggested. 



Can the behavior of Amoeba be resolved throughout into direct 

 unvarying reactions to simple stimuh, — into elements comparable to 

 simple reflexes ? 



For most of the behavior described in the preceding pages the stimuli 

 can be recognized in simple chemical or physical changes in the environ- 

 ment. Yet there are certain trains of action for which such a resolution 

 into unvarying reactions to simple stimuli seems unsatisfactory. This 

 is notably true for some of the food reactions. In watching an Amoeba 

 following a rolling food ball, as in Fig. 19, one seems to see the animal, 

 after failing to secure the food in one way, try another. Again, in the 

 pursuit of one Amoeba by another, it is difficult to conceive each phase 

 of action of the pursuer to be completely determined by a simple present 

 stimulus. For example, in Fig. 21, after Amoeba b has escaped com- 

 pletely and is quite separate from Amoeba c, the latter reverses its 

 course and recaptures b (at 11-13). What determines the behavior of 

 c at this point ? If we can imagine all the external physical and chemi- 

 cal conditions to remain the same, with the two Amoebae in the same 

 relative positions, but suppose at the same time that Amoeba c has never 

 had the experience of possessing b, — would its action be the same ? 

 Would it reverse its movement, take in b, then return on its former 

 course? One who sees the behavior as it occurs can hardly resist the 

 conviction that the action at this point is partly determined by the 

 changes in c due to the former possession of b, so that the behavior is 

 not purely reflex. 



Of less interest than the case just mentioned are modifications in 

 beliavior due to accUmatization, and to the interference of stimuli. 

 Amoeba may become accustomed to certain things, so as to cease reacting 

 after a time, though the condition remains the same. Thus Verworn 

 (1889 b) found that Amoebae which at first react to a weak electric cur- 

 rent may after a time continue their usual movements, without regard 

 to the current. Harrington and Learning (1900), as we have seen, found 

 that white or blue light thrown on Amoeba causes it to cease moving, but 

 if the light is continued, the movements begin again after a time. In- 

 deed, we have recognized above the general fact that change is the chief 



