-30- 

 formation of the "unified impulse". 



The responses of a starfish to stimuli, in so far as they 

 involve locomotion, may be divided into two categories, positive 

 responses, in which the resulting locomotion is toward the 

 stimulus, and negative responses, in which the direction of 

 locomotion is aw->y from the stimulus. Gentle contact at the 

 ti of the ray will usually elicit a positive response while a 

 negative response usually results from severe prodding or pinching. 



General statement of the mechanism oJT the positive response. 



The mechanism of the positive responses, is as I see it 

 as follows? A gentle contact stimulation of the tube feet at the 

 end of a ray causes these tube feet to extend in the direction 

 of the stimulus as we have already seen, other tube feet behind 

 this coordinate in this action, and receiving the contact 



.. i i ' i "Hi > ** 



stimulation of the substrate execute the step reflex* The 

 impulse to coordinate with the active tube feet at the tip of the 

 stimulated ray this spreads to the rest of the starfish, involving 

 after a time every tube foot in the body in coordinated locomotion. 



General description of the negative response. 



The negative response is brought ab*at on exactly the 

 same principle. The prodding or pinching of a certain ray 

 results in the retraction or inactivation of the tube feet in 

 that region and aa> &p^3a@W)s&8& vo the spread of this impulse, 

 to certain of the other tube feet. The extent of the spread is 

 of course determined by the strength of the stimulus* 



Assuming first that the stimulation is severe enough to 

 cause all the tube feet to retract or become inactive, H 



the first tube feet to resume their normal function are 



those farthest away from the source of stimulation. In this 

 experiment the tube feet farthest away are those of the opposite 

 ray tips. These tube feet are ori'rlejted in the direction of their 



