1907] Jennings. — Behavior of the Starfish. 137 



This factor may play an important part, but it is by no means 

 necessarily decisive. If the starfish is so deposited that the dorsal 

 side of a certain pair of rays comes in contact first, the animals 

 will usually turn in more cases toward these rays than in any 

 other given direction. But there are many other factors that may 

 determine the direction of turning in despite of this one. The 

 direction of the light often overcomes the present factor. In- 

 deed, any of the factors or combinations of factors to be men- 

 tioned may have this effect. In particular, it may be said that 

 any factor which has determined the direction of the impulse 

 before the dorsal surface of the rays has come in contact, will 

 determine the direction of turning. Any factor, to act decisively, 

 must come into action before the impulse is once set. After this, 

 the direction of turning can be changed only with great diffi- 

 culty. 



(4) Side of the rays that first come in contact. — If the star- 

 fish is deposited in a tilted position, so that a certain side of a 

 ray, or of two rays, touches the bottom first, then often all the 

 tube feet of those rays incline at once toward that side, and tend 

 to attach themselves. This is then followed by a similar action 

 of the tube feet of all the rays; they incline toward that side 

 (as in fig. 13). Thus a unified impulse has appeared. This 

 factor is often overcome by others; it plays a part if it comes 

 into action by itself at the moment when the impulse is to be 

 determined. 



(5) Tilting of the body. — If the starfish is placed on its back 

 in a tilted position, one side being a little elevated, this may 

 determine the direction of turning. This is because the tilting 

 tends to cause the lower rays to come in contact first, — determin- 

 ing the direction of the impulse in the way mentioned in para- 

 graphs (3) and (4). The mere inclination of the body in itself 

 seems to be of no effect. In a large number of experiments the 

 starfish was placed on plane surfaces inclined at various angles. 

 There was no tendency to turn in righting with any special ref- 

 erence to the direction of inclination. The surfaces being plane, 

 the rays were not more likely to touch sooner in one direction 

 than another. 



(6) Contact with a small object.— The starfish was placed 



