178 BEHAVIOR OF THE LOWER ORGANISMS 



to the carmine grains by contracting or by leaving its tube must be differ- 

 ent in some way from the organism which reacted to the same stimulus 

 by bending to one side. No structural change is evident, so that all 

 we can say is that the physiological state 0} the organism lias changed. The 

 same organism in different physiological states reacts differently to the 

 same stimuli. It is evident that the anatomical structure of the organ- 

 ism and the different physical or chemical action of the stimulating 

 agents are not sufficient to account for the reactions. The varying physio- 

 logical states of the animal are equally important factors. In Stentor 

 we are compelled to assume at least five different physiological states to 

 account for the five different reactions given under the same conditions. 

 We shall later find much occasion to realize the importance of physiologi- 

 cal states in determining behavior. 



These relations may be stated from another point of view, which 

 leads to interesting questions. The present physiological state of an 

 organism depends upon its past history, so that we can say directly 

 that the behavior of such an organism as Stentor under given conditions 

 depends on its past history. This statement we know is markedly 

 true for higher organisms. What a higher animal does under certain 

 conditions depends upon its experience : — that is, upon its past history. 

 In the typical and most interesting case we say that the behavior of the 

 higher organism depends upon what it has learned by experience. Is 

 the change in the behavior of Stentor in accordance with its past history 

 a phenomenon in any wise similar in character to the learning of a higher 

 organism? In judging of this question we must rely, of course, entirely 

 upon objective evidence ; — upon what can be actually observed. 

 When this is done, it is hard to discover any ground for making a dis- 

 tinction in principle between the two cases. The essential point seems 

 to be that after experience the organism reacts in a more effective way 

 than before. The change in reaction is regulatory, not merely hap- 

 hazard. And this is as clearly the case in Stentor as in the higher 

 organism. It is true that, so far as we can see, the behavior of Stentor 

 shows in only a rudimentary way phenomena that become exceedingly 

 striking and complex in higher organisms. Stentor seems to vary its 

 behavior only in accordance with the experience that either (1) the 

 stimulus to which a strong reaction is at first given, does not really 

 interfere with its activities, so that reaction ceases; or (2) that the reac- 

 tion already given is ineffective, since the interference with its activities 

 continues, so that another reaction is introduced. 1 If the changes in 



1 It is to be noted that nothing is said in this statement as to the Stentor's perceiving 

 these relations. The statement attempts merely a formulation of the observed facts in 

 such a way as to bring out their relation to what we observe in higher organisms. 



