586 Journal of Coviparativc Neurology and Psychology. 



are recognizable usually as successive phases of the reactiou (initial 

 shock and final tropic effect). 



4. Shock effects consist of shrinking movements which range in 

 intensity from local retractions of the more irritable ends to general 

 movements of the body. The latter are especially v^ell developed in 

 Perichaeta. These movements are single only in their weak form, 

 as with increase of the stimulus is developed a tendency to a rapid 

 succession of contractions. High states of muscular tension are 

 unstable in the earthworm, unlike those animals which Can roll into 

 a ball for defence. 



5. The degree of stimulation and the resulting shrinking move- 

 ments give rise to a progressive series of negative reaction types. 

 In type II shrinking back of the anterior end interrupts forward 

 movement only temporarily. In type III it is interrupted longer 

 while backward creeping takes place. In type IV both ends are 

 affected and stop extension, which goes on in the less irritable middle 

 region causing the rolling movement. Sidewise extension causes 

 stretching and some twisting and the ends initiate the righting 

 movements. Rolling is followed by backward crawling usually, 

 then by crawling forward. In type V the maximal stimulus causes 

 the cutting out of the intermediate forms of movement, rolling and 

 creeping backward, and instead the worm creeps forward at once, 

 the movement for which it is best adapted by its musculature. With 

 a maximal stimulus the posterior end and middle are more thoroughly 

 inhibited from extension than the anterior. 



6. With a series of graded stimuli the reaction types attain their 

 greatest frequency, as shown statistically, under different degrees of 

 stimulation. Each type exhibits increase of intensity with the 

 stimulus. 



7. Owing to the fact that the tropic response appears by itself only 

 as the result of a very Aveak stimulus or as a secondary effect of a 

 stronger one after its strength has subsided, this reaction is likely to 

 be counteracted by internal factors. Hence in respect to the tropic 

 response the behavior appears determined by the external stimulus 

 in a somewhat less degree than in many animals. 



8. Owing to the low receptivity for light, shock effects are infre- 



