240 THE BEHAVIOR OF LOWER ORGANISMS. 



with the revolution on the long axis. As a consequence, the anterior 

 end is swung about in a wide circle ; the organism tries successively 

 many widely differing directions (Fig. So). From each of these direc- 

 tions, as we have seen, a sample of water is brought to the sensitive 

 anterior end or mouth. Thus the reaction in itself consists in trying 

 the water in many different directions. As long as the water coming 

 from these various directions evinces the qualities which caused the 

 reaction the greater heat or cold or the chemical the reaction, with 

 its swinging to one side, continues. When a direction is reached from 

 which the water no longer shows these qualities, there is no further 

 cause for reaction ; the strong swerving toward the side A* ceases, and 

 the organism swims forward in the direction toward which it is now 

 pointed. It has thus avoided the region where the conditions were 

 such as to produce stimulation. 



While the account just given shows the essential features of the reac- 

 tion, the actual series of events appears in many cases more complicated, 

 though there is nothing differing in principle from what was just set 

 forth. The apparently greater complication arises from the repetition 

 of that feature of the reaction which consists in swimming backward, 

 and in the cessation of the reaction at intervals, with an attempt to 

 swim forward. After the organism has swung the anterior end to one 

 side, if it still receives the stimulus it may begin the reaction anew ; 

 that is, it may swim backward a distance, and again begin turning 

 toward the side A'. This may be repeated several times. Each time 

 it is repeated the organism swings its anterior end through a new series 

 of positions, thus increasing the chances of finding one in which there 

 is no farther stimulation. Again, the organism, after reacting in the 

 way described in the last paragraph, may begin to swim forward, only 

 to find that it receives the stimulus again ; it then repeats the whole 

 reaction, thus supplying itself with a completely new set of directions 

 and of samples of water from those directions. In some cases the reac- 

 tion is thus repeated many times before any direction is found toward 

 which the organism can swim without receiving stimulation. 



This is the method of behavior which the present author has been 

 describing in detail in many organisms in his series of ten Studies on 

 Reactions to Stimuli in Unicellular Organisms,* and in the foregoing 

 Contributions to the Study of the Behavior of the Lower Organisms. 

 Not until recently, it must be confessed, has the real significance of 

 this type of behavior been fully perceived. The results seemed to a 

 large degree negative ; the reaction method clearly did not agree with 

 the prevailing tropism theory, nor with any other of the commonly 



* Journ. of Physiol., 1897, vol. 21; Amer. Journ. of Physiol., vols. 2 to 8, 

 1899 to 1902; Amer. Naturalist, vol. 33, 1899; Biol. Bull., vol. 3, 1902. 



