THE REACTIONS OF ORGANISMS TO LIGHT 215 



of Bohn and Loeb in all of their recent papers referring to this 

 subject. And this in spite of the fact that in the numerous 

 descriptions of orientation by this method given by Jennings 

 and myself no such factors whatever are involved or implied. 



The main difficulty these authors have in grasping the subject 

 lies in their assumption that locomotion is dependent upon the 

 same factors which regulate the direction of locomotion, an 

 assumption for which, as far as I am aware, there is absolutely 

 no evidence. 



Let us attempt to clear up these matters by means of an illus- 

 tration : Suppose an active blind fish be put into an enclosure 

 with a small opening at one side leading into a long narrow 

 straight passage. The fish swims about, strikes the wall of the 

 enclosure, turns and takes another course, strikes the wall again, 

 then proceeds in a different direction, etc., until finally it strikes 

 the opening and enters the narrow passage. The fish has become 

 oriented and if there is nothing to turn it out of its course it 

 may proceed through the passage without further stimulation, 

 but if it is turned out of its course it strikes the wall of the passage, 

 turns and soon becomes oriented again. Surely no one will 

 maintain that it is necessary to assume " symmetrical stimula- 

 tion " and " retention of impressions " of the various movements 

 in order to account for the orientation of the fish. And what 

 basis is there for the assumption of psychic factors! It would 

 indeed be a comparatively simple task to construct a machine 

 with wheels and springs and levers so arranged that after strik- 

 ing an obstacle it would back off and take a different course, 

 and if put into an enclosure similar to that assumed in case of 

 the fish it would finally strike the opening and become oriented. 

 As far as trial movements are involved in the orientation of fly 

 larvae or earthworms the process is, in principle, precisely like 

 this. The organism just like the hypothetical machine or the 

 blind fish in the enclosure continues to turn in different directions 

 assuming different axial positions until the stimulus which causes 

 the turning ceases. And the same principle is involved in every 

 account of orientation by trial in the lower organisms that has 

 been given either by Professor Jennings or myself . Note, e. g., the 

 following statement from Jennings quoted in my book, p. 47: 

 " [The so called trial and error method of orientation] consists 

 in successively ' trying ' not only different directions of locomo- 



