230 BEHAVIOR OF THE LOWER ORGANISMS 



results seems to be as follows : The nervous system forms a region in 

 which the physiological changes resulting in activity take place more 

 readily and rapidly than in other parts of the protoplasm. These 

 changes occur in the nervous system more readily both as a result of the 

 action of external stimuli, and under the influence of changes in neigh- 

 boring parts of the body. Hence parts containing the nervous system 

 are more sensitive to external stimulation than other parts of the body, 

 and they serve to transmit stimulation more readily. Furthermore, 

 the spontaneous changes occurring in the protoplasm, which result in 

 the production of rhythmical contractions, are more pronounced and 

 rapid in the nervous system than elsewhere, so that the rhythmical 

 contractions usually begin in parts containing nerve cells. But the 

 difference between nerve cells and other cells is only quantitative in 

 character. The peculiar properties of the nerve cells are properties of 

 protoplasm in general, but somewhat accentuated. 



11. Some General Features of Behavior in Ccelenterates 



Comparing the behavior of this low group of multicellular animals 

 with that of the Protozoa, we find no radical difference between the two. 

 In the ccelenterates there are certain cells — the nerve cells — in which 

 the physiological changes accompanying and conditioning behavior 

 are specially pronounced, but this produces no essential difference in 

 the character of the behavior itself. As in the Protozoa, so here, we 

 find behavior based largely on the process of performing continued or 

 varied movements which subject the organism to different conditions 

 of the environment, with selection of some and rejection of others. 

 We find the same changes in behavior under a continued intense stimu- 

 lus, determined by changes in the physiological condition of the animal. 

 We find at the same time many reaction movements of a fixed character, 

 dependent largely on the structure of the organism, as we do in bacteria 

 and infusoria. Many of these specific responses to specific stimuli 

 are so definitely adapted to the precise conditions under which the 

 organism lives that we can hardly resist the conclusion that they have 

 been developed in some way under the influence of these conditions, 

 as a result of the fact that they are beneficial to the organism. Such, for 

 example, is the quick though complicated grasping and feeding reaction 

 by which Gonionemus responds to a moving object. Possibly such 

 determinate reactions have arisen through fixation of movements which 

 were originally reached by a process of trial, — a possibility to which 

 we shall return in our general analysis of behavior. 



In the Ccelenterata we find also, as in Amoeba, a certain number of 



