584 Journal of Coinparative Neurology and Psychology, 



When reactions to light are compared with those to other stimuli 

 to which the earthworm is more responsive it becomes evident that 

 a distinguishing feature of the light reactions is the relative absence 

 of shock effects, as denoted by shrinking, and we conclude that 

 changes of intensity must be communicated to and through the photo- 

 receptors too slowly to be effective as an immediate stimulus, even 

 though tonic effects may become quite apparent " after a sufficient 

 interval. 



Note on Experiments with Electrical Stimulation. 

 The experiment was tried of stimulating with an electric current 

 gradually by means of a rheonom. A tetanizing current was used. 

 For 'electrodes a small piece of sponge saturated with water was 

 fastened over the platinum tips. The instrument was so adjusted 

 that with the arms of the rheonom in the maximum position the 

 current caused retraction of the head. The stimulus was then intro- 

 duced while the arms of the rheonom were being rotated from mini- 

 mum to maximum position. It was possible with the current thus 

 gradually introduced to obtain a turning response instead of shrinking. 



Conclusions. 

 The interpretation of shrinking movements as unterschiedsemp- 

 findlich reactions is manifestly supported by their time relation to 

 the stimulus in all cases and their sudden character. The tropic 

 response is not a sudden movement and it may be preceded by a 

 slight pause, as shown above under type I. The only exception to 

 the last statement is found in connection with the sharp turning 

 response designated as the "end for end" reaction under type V. 

 But this was explained to be a fused shrinking and turning move- 

 ment. The same kind of a reaction of a weaker form is found in 

 the transitional response from type I to II in which the turning 

 movement is more sudden and accompanied by shrinking back. In 

 type II, however, after the initial sharp recoil of the head there 

 may be a slight pause and the subsequent turning is a quiet move- 

 ment. It may be said then that turning movements of the anterior 

 end are never indicative of shock except when combined (fused) with 



