BEHAVIOR OF CCELENTERATA 231 



responses due to the simple, direct reaction (by contraction) of the part 

 affected by a local stimulus. Where such simple and perhaps primi- 

 tive reactions are advantageous to the organism, they are preserved as 

 important factors in behavior, as in the negative reactions of medusae. 

 Where they are not advantageous to the organism, they are replaced, 

 supplemented, or followed by more complicated reactions, so that they 

 form a comparatively unimportant feature in the behavior of most of 

 these animals. 



In ccelenterates we find. the same dependence of behavior on the 

 physiological state of the organism that we found so marked in Pro- 

 tozoa. The same organism does not react always in the same way to 

 the same external conditions. In the preserlt group the dependence of 

 behavior on the progress of the internal physiological processes, par- 

 ticularly those of metabolism, stands out strongly. The animal in which 

 material for the metabolic processes is abundant differs radically in its 

 behavior from the hungry specimen. The reaction to a given stimulus 

 depends not alone on the anatomical structure of the animal and the 

 nature of the stimulus, but also upon the way the internal processes 

 are taking place. We cannot predict how an animal will react to a 

 given condition unless we know the state of its internal physiological 

 processes, and often whether a positive or negative reaction will help 

 or hinder the normal course of these processes. The external processes 

 of behavior are an outgrowth and continuation of the. internal processes. 



The state of the organism as regards its metabolic processes seems 

 indeed the most important determining factor in its behavior. Certain 

 internal metabolic states drive the animal, without the action of any 

 external agent, to the performance of long trains of activity, of exactly 

 the same character as may also be induced by external stimulation. 

 The state of the metabolic processes likewise determines the general 

 nature and the details of the reactions to external stimuli. It decides 

 whether Hydra shall creep upward to the surface and toward the light, 

 or shall sink to the bottom ; how it shall react to chemicals and to solid 

 objects; whether it shall remain quiet in a certain position, or shall 

 reverse this position and undertake a laborious tour of exploration. It 

 decides whether the sea anemone shall react to indifferent bodies, and 

 to food, by the long and complex "food reaction" or the equally long 

 and complex "rejecting reaction." It determines whether Cerianthus 

 shall remain quietly in its tube in the sand, or shall seek a new abode. 

 Innumerable details of behavior are determined in the ccelenterates 

 by this factor. 



The same dependence of behavior on the metabolic processes of the 

 organism we have seen in the Protozoa, and especially in the bacteria. 



