1907] Jennings. — BcJiavior of the Starfish. 1-47 



"obstinate," persisting' in turning in a certain way in spite of 

 all sorts of opposition. In others the direction of the impulse 

 is changed much more readily. Sometimes when the attached 

 rays are forcibly released, the direction of the impulse at once 

 changes, though this is not usually the case. The strength of 

 the impulse varies even in the same individual. If the direction 

 of the impulse has been changed several times by outside inter- 

 ference, it often after a time becomes strongly set, and is no 

 longer influenced by the conditions which at first changed it. 

 : , It seems to be a general rule that the impulse is not so firmly 

 set when it is first formed, as later. Often when a starfish is 

 turned on its back, a common impulse appears after a short 

 period of uncoordinated struggling; all the tube feet turn to- 

 ward a certain side. Suddenly this impulse is seen to change, 

 all the tube feet inclining in a different direction, and the star- 

 fish beginning to turn that way. The impulse may often be 

 changed with great readiness in this period immediately after it 

 is formed, by stinuilating certain rays, or the like. But again, 

 in some cases the impulse is strongly set at the beginning, and can 

 not be changed without strong and repeated stimulation. 



A formed impulse may usually be caused to disappear by 

 lifting the starfish from the bottom and holding it suspended 

 in the Avater, back downward, a minute or two. At first it 

 usually attempts to continue turning in the way already begun. 

 But its tube feet and rays not coming in contact with anything, 

 it soon gives this up ; the coordinated impulse disappears, and all 

 the rays and tube feet begin to feel about in various directions. 

 A new impulse may then be determined by some object with 

 which a certain ray comes in contact. 



Indecision. — Since there are so many factors any one of 

 which may determine the direction of the impulse if it acts at 

 the moment of instability, there is of course little chance that 

 the direction of turning will be left long undecided. Yet there 

 are often a few moments of uncertainty, and in rare cases the 

 factors tending to cause turning in opposite directions are so 

 evenly balanced that a more prolonged period of indecision 

 results. 



