126 THE BEHAVIOR OF LOWER ORGANISMS. 



may properly characterize the physiological condition which produces 

 the negative reaction to strong stimuli, with Professor J. Mark Bald- 

 win (1897, p. 43) as the " physiological analogue of pain." This, of 

 course, by no means commits us to the belief that the organisms have 

 a sensation of pain ; concerning this we know nothing. 



It thus seems to me possible to trace some of the physiological con- 

 ditions which we know, from objective evidence, to exist in man and 

 the higher animals, back to the lowest organisms. Many conditions that 

 we can clearly distinguish in man will doubtless be followed back to a 

 common single condition in the lower organisms ; but this is exactly what 

 we should expect. Differentiation takes place as we pass upward in 

 the scale, in these matters as in others. 



The most interesting and important field in which we find the 

 behavior of higher organisms dependent on their previous history, and, 

 therefore, on their present condition as influenced by previous experi- 

 ence, is in that group of phenomena which we call memory, or learning 

 by experience. Memory has as its basis the general phenomenon that 

 a stimulus received or a reaction performed leaves a trace on the 

 organism, or modifies its condition in such a way that it later reacts 

 differently to the same stimulus. This basis of memory is, of course, 

 clearly present in Stentor. 



The analysis of the different physiological conditions found in the 

 lower organisms, the influences to which they are due, and the 

 reactions of these organisms as influenced by physiological conditions 

 certainly forms a most promising field for research, and one as yet 

 almost untouched. 



SUMMARY. 



The present paper attempts to show, by an analysis of certain 

 phenomena in the behavior of lower organisms, taking Stentor and 

 Planaria as types, that physiological states of the organism are most 

 important determining factors in reactions and behavior. In these 

 organisms, to the same stimuli, under the same external conditions, 

 the same individuals react at different limes in radically different ways, 

 showing the existence of different physiological states of the organism, 

 which determine the nature of the reactions. In a unicellular organ- 

 ism (Stentor) we can distinguish at least six different physiological 

 states, in each of which the organism has a different reaction method, 

 and corresponding facts are brought out for the flatworm. Scattering 

 observations taken from works on tropisms, etc., are shown to indicate 

 that the same state of affairs is found in other lower organisms. 



The conditions producing these different physiological states are 

 examined and their importance for the theory of behavior in the lower 

 organisms is brought out. The relations of these facts to " interference 



