62 Studies in Animal Behavior 



not guided by a mere reflex response, but had an 

 awareness of the general space relations of its re- 

 gion, the relative position of the light and itself and 

 of the movements necessary to bring itself toward 

 the light. If such a general topographical sense 

 seems too high a psychical endowment to be cred- 

 ited to so simple a creature, it must be remembered 

 that other insects, notably the bees and wasps, have 

 a much more definite and detailed cognizance of the 

 topographical relations of their environment than 

 anything in the behavior of Ranatra would call for. 

 Simple and mechanical as much in the light reactions 

 of Ranatra seems to be, there are many features of 

 its phototaxis which are very difficult to explain 

 on the basis of simple reflex orientation. 



We might expect a priori to find that somewhere 

 in the course of evolution the tropisms become more 

 or less subordinated to higher forms of behavior. 

 It is quite evident that much in the behavior of 

 animals may be explained as a more or less simple 

 manifestation of phototaxis, geotaxis, chemotaxis, 

 and so on. The daily depth migrations of pelagic 

 animals is traceable, to a considerable degree, to 

 variations in the sense of the response to light and 

 gravity. One circumstance that leads copepods to 

 swim to the surface at night and go down in the 

 daytime is because they are positive to weak light 

 and negative to strong light. The negative reac- 

 tion of centipedes, termites and many other organ- 

 isms keeps them in dark and secluded situations. 



