ANALYSIS OF BEHAVIOR IN LOWER ORGANISMS 299 



the hungry Hydra reacts positively to chemicals. In certain physio- 

 logical conditions the flatworm reacts positively to almost any stimulus. 

 At other times the opposite conditions prevail; the animal reacts nega- 

 tively to the stimulus to which it before reacted positively. In closely 

 related organisms differing in their metabolic processes, the reaction to 

 a given agent depends on the nature of the metabolic processes, tending 

 to retain the conditions favoring these processes. This is especially 

 well illustrated in the bacteria (pp. 36, 39) and in the ccelenterates 

 (pp. 224, 231), but is equally true for other organisms. Thus what the 

 organism does depends on the course of its life processes, and upon the 

 completeness or incompleteness of their performance. In other words, 

 the behavior of the animal under stimulation corresponds to its needs, 

 and is determined by them. This correspondence is of course not al- 

 ways perfect ; with this point we can deal after we have considered the 

 nature of the reactions given. But a study of the determining factors 

 of behavior demonstrates that the relation of external conditions to in- 

 ternal processes is the chief factor, and that hence behavior is regulatory 

 in essential nature. 



(6) We may sum up the external factors that produce or determine 

 reactions as follows: (1) The organism may react to a change, even 

 though neither beneficial nor injurious. (2) Anything that tends to 

 interfere with the normal current of life activities produces reactions of 

 a certain sort ("negative"). (3) Any change that tends to restore or 

 favor the normal life processes may produce reactions of a different sort 

 ("positive"). (4) Changes that in themselves neither interfere with 

 nor assist the normal stream of life processes may produce negative or 

 positive reactions, according as they are usually followed by changes 

 that are injurious or beneficial. (5) Whether a given change shall pro- 

 duce reaction or not, often depends on the completeness or incomplete- 

 ness of the performance of the metabolic processes of the organism 

 under the existing conditions. This makes the behavior fundament- 

 ally regulatory. 



