3o8 Journal of Comparative Neurology and Psychology. 



the various objects that come into its field of vision, it is cer- 

 tainly something more than a mere reflex machine. In organ- 

 isms which are capable of a higher type of response we should 

 at least be on our guard in attempting to explain their tropisms 

 as due entirely to direct reflexes involuntarily performed in re- 

 sponse to outer stimuli. The conduct of higher animals is 

 guided in large measure by their likes and dislikes, however we 

 may interpret this kind of behavior in physiological terms. 

 Between such behavior and those tropisms which are the result 

 of comparatively simple reflexes there are, no doubt, numerous 

 intermediate kinds of conduct. It is not unreasonable to sup- 

 pose that tropisms which in low forms are brought about by 

 direct reflexes may in higher animals complicate into reactions 

 of the pleasure-pain type while still preserving outwardly the 

 appearance of a more mechanical mode of response. At the 

 same time an element of direct reflex action may be retained, 

 although closely associated with and capable of being modified 

 by more complicated neural processes. A consideration of the 

 experiments described in this paper will lead us, I think, to 

 some such view. 



II. General Habits. 



Ranatras are generally found in ponds or streams among 

 masses of vegetation where they lie quiet the greater part of the 

 time. Although capable under certain conditions of manifest- 

 ing considerable activity, these insects are usually sluggish in 

 their movements. Their choice of habitat is probably deter- 

 mined, in great part at least, by their positive thigmotaxis, 

 since they tend to insinuate themselves between objects which 

 afford considerable contact stimuli. Their habit of coming 

 together to form groups is a manifestation of the same tenden- 

 cy. When several individuals are placed in an aquarium they 

 mass together when at rest to form a cluster in which they are 

 often so closely aggregated and so tangled together that those 

 which are near the center of the group experience much diffi- 

 culty in disengaging themselves. In this way they may lie for 

 n an almost motionless state. 



