470 H. S. Jennings. 



Clearly, the holding of any given position depends, not on the 

 relation of the body to any one or two sources of stimulation, but 

 on the proper maintenance of the natural physiological processes of 

 the organism. The actinian does not always maintain a certain 

 position with relation to gravity, nor does it always keep its body 

 straight, nor its foot in contact, nor its body surface in contact. 

 It does not at all times receive food. It may remain quiet for 

 considerable periods with one or more conditions lacking. The 

 organism tends on the whole to take such a position as is most 

 favorable to the unimpeded course of its natural physiological 

 processes. Certain usually required conditions may be dispensed 

 with provided other favorable ones are present. The behavior, 

 like that of higher animals, represents a compromise of the various 

 needs imposed upon the animal by its physiological processes. 



Examination of the literature shows that throughout the Coelen- 

 terates there is a similar dependence of behavior on the progress of 

 the internal physiological processes, particularly those of metab- 

 olism. The state of metabolism decides whether Hydra shall creep 

 upward to the surface or shall sink to the bottom (Wilson '91), 

 how it shall react to chemical and to solid objects (Wagner '05), 

 whether it shall remain quiet in a certain position, or shall reverse 

 this position and undertake a laborious tour of exploration. In 

 the sea anemones it determines, as we have seen, even the details 

 of long trains of reaction. The state of the metabolic processes 

 appears to be the most important determining factor in the 

 behavior of Ccelenterates. 



The same dependence of behavior on the internal physiological 

 processes is found in other groups, even in those much lower than 

 the Ccelenterates — the Protozoa, and particularly the Bacteria. 

 This is brought out especially in some of the work ot Engelmann. 

 A number of examples of this relation will be given in the paper 

 which follows the present one, so that they may be omitted here. 

 The fact that in higher animals behavior depends largely on hunger 

 and satiety is, of course, so well known that it need not detain us. 



The relation of behavior to the internal physiological processes, 

 of which we have given some examples in the foregoing pages, is 

 manifestly of the greatest significance for the understanding of 

 behavior. The facts adduced show directly that in many cases 

 the determining factor in reactions to stimuli is not the anatomical 

 configuration of the body, taken in connection with simple laws 



