190"] Jennings. — Behavior of the Starfish. 113 



results were the same. Moreover, the movement toward the 

 opaque sides of the containing vessel could not be explained in 

 this way. 



But one fact needs emphasis. The number of individuals 

 experimented on in this way was small (only about a dozen), 

 and fully half of these moved without any refere7icc to the po- 

 sition of the plate or screen. Yet those that did respond, reacted 

 so constantly and clearly that the results can hardly have been 

 accidental. Statistical work with a large number of individuals 

 will be required to set this matter in a perfectly clear light. The 

 M'ork with light was subsidiary to the main objects which I had 

 in view, and therefore this matter could not be investigated thor- 

 oughly in the time at my disposal. But I believe that all the 

 facts herein set forth are new in the behavior of starfish toward 



light. 



Positive Reactions. 



Not only does the starfish retreat from those things that tend to 

 interfere with its physiological processes, but it follows up those 

 which assist these processes. It follows food, either on coming 

 in contact with it, or when it is reached by characteristic chemical 

 stimuli from the food; this has already been discussed (pp. 

 84-94). The reaction is, as we have seen, not a stereotyped, irre- 

 sistible tropism ; the animal frequently feels about a great deal 

 before it finds the food. A typical example of this is given in our 

 account of the food reactions (p. 93). 



Positive reactions take place toward indifferent objects, such 

 as stones, depressions, roughenings of the surface, etc., when the 

 circumstances are such that movement toward these objects is 

 likely to be advantageous. These are reactions to what I have 

 elsewhere (1906) called representative stimuli, — the present 

 stimulus not being beneficial in itself, but leading to or repre- 

 senting the beneficial results that follow upon a positive reaction 

 toward it. Examples of such reactions are given in a later section 

 (p. 114). 



In the positive reactions, as in the negative ones, the star- 

 fish usually moves with a unified impulse, — all the tube feet of all 

 the rays being directed toward the object toward which the star- 

 fish is moving. 



