70 H. G. Kribs 



the force of the stimulated reflex. As the chemical becomes more 

 and more dangerous to the organism, the initial reflex, developed 

 upon contact with the chemical, throws the animal ever further 

 away from its influence. Is this reaction due to an increase in con- 

 trol of the movements of the animal by the lines of diflFusion, or is 

 it because the vigor of the reflex is proportionate to the amount of 

 energy liberated by the impinging stimulus? It seems most clear 

 that the latter suggestion, only, can be adjusted to all the data 

 here involved. 



When the stronger stimulus is applied to the mid-sections of the 

 body the reflexes are always ventral — irrespective of the exact 

 locus of stimulation or the direction from which the chemical may 

 come. This reflex tends to bring the head and caudal segments 

 together. Sometimes this serves also to bring the prostomium 

 nearer to the source of the stimulus. A counter reflex is then 

 given, characteristic of the regular prostomial stimulation-reflex, 

 which throws the anterior end away from the chemical, and if the 

 stimulus is not too strong, the animal escapes. 



The movements given in response to the different chemicals 

 vary within very wide limits. Each group of chemical stimulates 

 reactions peculiar to themselves. Throughout the whole series, 

 the ability of the animal mechanism to adjust itself to the impinge- 

 ment of a chemical upon the bodv wall (excepting the anterior 

 segment) varies inversely as the strength of the chemical. This 

 phenomenon is practically reversed in the case of prostomial stimu- 

 lations. In these cases we have what we may call a prostomial 

 reflex which is inherently negative and which serves a fundament- 

 ally regulatory function as the animal approaches a marked change 

 in the environmental conditions. 



These facts show conclusively that the prohlem of animal beha- 

 vior must look for its solution in the physiological arrangement of 

 the protoplasmic, aggregates of the organism under investigation. 

 So far as external stimuli are concerned we may conclude: 



I. The sort of stimulus does not predetermine the reaction 

 that will follow upon its impingement upon any part of the organ- 

 ism, although it may contribute a significant thrust to that reac- 

 tion. 



