274 BEHAVIOR OF THE LOWER ORGANISMS 



ordinated reaction of the organism as a whole, depending for its existence 

 on an entirely normal physiological condition" (Pearl, 1903, p. 619). 



Similar lack of uniformity and simplicity appears in the remainder 

 of the behavior of the flatworm. In few of the lower metazoa has the 

 movement been so thoroughly analyzed as in Planaria. But there seems 

 to be no reason for thinking that in this simple animal these relations are 

 more complex than in most invertebrates. 



The recent thorough studies of Radl (1903) on reactions to light in 

 many animals have shown clearly the inadequacy of this theory to ac- 

 count for most of the reactions to this agent. Bohn (1905) has likewise 

 been compelled to reject this theory, on the basis of the results of his 

 thorough studies on the behavior of the animals of the seashore. To 

 the writer it appears that most of the recent thorough work on animal 

 behavior points in the same direction. 



We must then conclude from our examination of the facts that for 

 the lower organisms taken into consideration in the present work, the 

 local action theory of tropisms is of comparatively little value for inter- 

 preting behavior. This theory uses and attempts to make of general 

 application certain elements here and there observable in the behavior 

 of some organisms. But in many organisms even these elements are 

 almost completely lacking, and in no organism that we have taken up 

 does this theory adequately express the nature of behavior. The tro- 

 pism as applied to animal behavior in the sense we have considered, is 

 not an elementary factor ; it is only a more or less artificial construction, 

 made by combining certain elements of behavior and omitting others 

 that are of most essential significance. It makes use of certain simple 

 phenomena that actually exist, but elevates these into a general explana- 

 tion of directed behavior, for which they are utterly inadequate. The 

 prevalence of this local action theory of tropisms as a general explana- 

 tion of behavior in lower organisms is based only on an incomplete knowl- 

 edge and an insufficient analysis of the facts of behavior. 



Other Terms employed in Accounts of Animal Behavior 



In the foregoing pages we have criticised a certain definite theory of 

 tropisms, this being the theory most commonly implied when the word 

 is used in a precisely defined way. But the term "tropism" is often 

 used in a looser sense. By some writers the word is applied merely to 

 the general phenomenon that the movements of organisms show definite 

 relations to the location of external agents. In this sense the word im- 

 plies no theory, and is not open to criticism on the basis of observed 

 facts. It is, of course, equally applicable to the behavior of man and 



