CHAPTER XVI 



ANALYSIS OF BEHAVIOR IN LOWER ORGANISMS 



i. THE CAUSES AND DETERMINING FACTORS OF MOVEMENTS AND 



REACTIONS 



IN the following sections we shall analyze the behavior of the lower 

 organisms described in previous chapters, attempting to determine the 

 essential characteristics of behavior and to bring out the chief factors 

 of which it is made up. We shall take up first the factors causing or 

 determining the movements and reactions, treating first the inner, then 

 the outer, factors. Then we shall consider the movements and reactions 

 themselves, attempting to bring out the features of essential importance. 

 From a synthesis of our results on both sets of factors the causes and 

 the effects we shall try to arrive at a general statement of the funda- 

 mental character of behavior in the lower organisms. 



The external factors in behavior are usually known as stimuli, and 

 their effects on movement as reactions. The term " reaction" has been 

 used in various ways. In our analysis we shall employ the word "reac- 

 tion" as signifying an actual change in movement. The word is some- 

 times used in a looser sense. For example, the movement toward a 

 source of light is often spoken of as the reaction to light, even though the 

 only observable change of movement was that by which orientation was 

 brought about. This looser sense is sometimes unavoidable, either from 

 our ignorance of the facts, or for other reasons ; when used in this loose 

 sense in the following, the context will clearly indicate it. Where ques- 

 tion might arise, reacton is to be understood as meaning an observable 

 change of movement. To avoid ambiguity, the latter phrase will some- 

 times be used in place of the word " reaction." The following discussion 

 will be intelligible only if this meaning of the word "reaction" is kept in 

 mind. 



A. The Internal Factors 



(i) Activity does not require Present External Stimulation. A first 

 and essential point for the understanding of behavior is that activity 

 occurs in organisms without present specific external stimulation. The 



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