68 H. G. Kribs 



conclusively that chemotoxis plays a very significant part in the 

 methods and processes of animal behavior. It shows, further, 

 that under conditions of control one may approximate the physio- 

 logical states which underlie the movements an organism may 

 exhibit in a state of nature. The various movements which we 

 have stimulated artificially, are of the nature of reflexes, more or 

 less complex. Many of these are so haphazard in their expression 

 that they seem to be merely the spontaneous play of various 

 amounts of energy, released within the mechanism of the animal. 

 On the other hand, some of these movements possess a certain 

 element of precision or adaptation which is manifestly beneficial 

 to the organism. They remove the organism from an injurious 

 environment in the quickest possible way. One of the first prob- 

 lems in Animal Behavior is: How did these more adaptive reflexes 

 arise in a state of nature? Our effort, therefore, will be to corre- 

 late the reflexes observed here under wider categories that will 

 help to interpret the action system of .'^^olosoma in a phylogenetic 

 way. Before we suggest a solution of our problem, however, it is 

 necessary to estimate carefully the modus operandi of the various 

 reactions involved. 



In the case of the threshold reactions, when the stimulus impin- 

 ged laterally upon the prostomium there followed a turning of the 

 head segment toward the source of stimulation. Was this turn- 

 ing due to the asymmetrical impingement of the lines of diffusion, 

 or to the electrolytic effect of moving ions upon the cell mem- 

 branes of that side of the head? In some way both of these factors 

 may have been involved. On the other hand it must be noted that 

 although the animal turned toward the side which was stimulated, 

 the angle in which the solution is projected toward the animal 

 through the pipette mav vary within enormous limits without 

 developing any variation in the side thrust of the reaction which 

 immediately follows. The prostomium is turned toward that 

 side which is first impinged upon by the chemical, regardless of the 

 direction from which that chemical may come. Again, after the 

 initial exploring reactidn has been expressed, with the exception of 

 the positive reactions, all of the succeeding movements have no 

 direct reference to the stimulus, its direction, or its source. 



