190'] Jennings. — Behavior of the Starfish. 115 



ward the light. Thus the usual reaction to light is completely 

 prevented or changed when the starfish comes into relation with 

 some object. 



Any marked inequality of the surface acts in the same way 

 as a solid object. If the tube feet find in their exploratory move- 

 ments a depression, the starfish moves toward this exactly as to- 

 ward a projecting object ; the animal tries to force itself into 

 the depression, seeming to endeavor to protect itself from the 

 light. 



As a result of these relations, when the starfish is subjected 

 to light while clinging to a rock or in a tide pool, its movements 

 are only indirectly determined by the direction of the rays of 

 light. If there are roughenings or depressions of the rocky sur- 

 face, the animal moves with reference to these, as well as with 

 relation to areas of light and shade ; it does not stop moving till 

 it has reached a place where it is no longer subjected to strong 

 light. 



2. Effects of Position of the Body. — The movements under 

 stimulation are partly determined by the position of the animal 

 at the time stimulation occurs. Thus, a specimen had taken an 

 elongated form, with three rays projecting in one direction, two 

 in the opposite, with a sort of narrow waist between them (as 

 in fig. 4). Now sunlight was allowed to fall on the animal trans- 

 versely to its (temporary) long axis. This roused the starfish to 

 activity, but the animal crept toward the middle one of the three 

 rays (c), — so transversely to the light. Gradually the rays 

 spread out ; the creature took the star form, and slowly veered 

 off, so as to finally move directly away from the source of light. 

 Examples of such dependence of the direction of movement on 

 the temporary form of the body could easily be multiplied. 



3. Persistence of Impulse to Move in a Certain Direction. — 

 We have already noticed the fact that when the starfish moves in 

 a certain direction, it does so under the effect of a unified im- 

 pulse**, which is seen in the coordinated position and movement 

 of all the tube feet, as well as in other ways (see pp. 97, 113). 

 Such an impulse, when once in operation, lasts for some time, in 



" I use the word impulse for lack of some better term, in a descriptive 

 sense, without intending to imply anything subjective behind the action; 

 concerning such we know nothing. 



