252 THE BEHAVIOR OF LOWER ORGANISMS. 



the reaction, and turned far toward the side on which the stimulus was 

 acting. Mast (1903) showed, as we have seen, that when the flatworm 

 is heated it tries successively almost every form of reaction which it 

 has at command. Such results have a most important bearing on the 

 problem of the relation of the reaction method to the stimulus. Neither 

 direct action of the stimulus on the motor organs as separate entities, 

 nor a typical fixed interconnection of sense organs and motor organs 

 can explain such results. As a result of continued strong stimulation 

 the organism passes from one physiological state to another, and each 

 physiological state has its concomitant method of reaction. 



The present paper may be considered as the summing up of the 

 general results of several years' work by the author on the behavior of 

 the lowest organisms. This work has shown that in these creatures 

 the behavior is not as a rule on the tropism plan a set, forced method 

 of reacting to each particular agent but takes place in a much more 

 flexible, less directly machine-like way, by the method of trial and 

 error. This method involves many of the fundamental qualities which 

 we find in the behavior of higher animals, yet with the simplest possi- 

 ble basis in ways of action ; a great portion of the behavior consisting 

 often of but one or two definite movements, movements that are stereo- 

 typed when considered by themselves, but not stereotyped in their 

 relation to the environment. This method leads upward, offering at 

 every point opportunity for development, and showing even in the 

 unicellular organisms what must be considered the beginnings of intel- 

 ligence* and of many other qualities found in higher animals. Tropic 

 action doubtless occurs, but the main basis of behavior is in these 

 organisms the method of trial and error. 



* Throughout this paper a number of terms are used whose significance as 

 they are commonly employed is determined by our subjective experience. But 

 all these terms (save those directly characterized as " subjective states," or 

 "states of consciousness") will be found susceptible also of definition from cer- 

 tain objective manifestations, and it is in this objective sense that they are used 

 in the present paper. Thus " perception " of a stimulus means merely that the 

 organism reacts to it in some way; " discrimination" of two stimuli means that 

 the organism reacts differently to them ; " intelligence " is defined by the objective 

 manifestations mentioned in the text, etc. These terms are employed because it 

 would involve endless circumlocution to avoid them; they are the vocabulary 

 that has been developed for describing the behavior of men, and if we reject them, 

 it is almost impossible to describe behavior intelligibly. When their objective 

 significance is kept in mind there is no theoretical objection to them, and they 

 have the advantage that they bring out the identity of the objective factors in the 

 behavior of animals with the objective factors in the behavior of man. 



