1907] Jennings. — Behavior of the Starfish. 141 



yet appeared. Now those rays which pull in a certain direction 

 are forcibly detached from the bottom by the experimenter, 

 whereupon the starfish begins to turn in the opposite direction, 

 — a unified impulse appearing. (After the impulse has ap- 

 peared, this releasing- of certain rays has little influence, as we 

 shall see later.) 



(12) Intense stimulation of certain rays. — After several rays 

 have become attached, some pulling in one direction, some in 

 another, the direction of the impulse may often be determined 

 by strongly stimulating certain rays, as by striking, pressing, or 

 pinching them. Thereupon these rays begin to detach themselves, 

 and the starfish turns toward the opposite side. 



(13) Impulse retained from, a previous reaction. — The direc- 

 tion of the impulse may have been determined in a given case 

 by any of the methods mentioned above. The starfish is thus 

 turning in a certain definite way toward a certain pair of rays. 

 We now release it from its attachment, remove it to a new place, 

 and place it in entirely different relations to the determining 

 conditions. Nevertheless, it now turns just as it had begun to 

 turn, toward the same pair of rays, the impulse once produced 

 persisting in the new reaction in spite of changed conditions. 



Again, the starfish may be allowed to finish righting itself, 

 the direction of the impulse having been determined in any one 

 of the ways described above. As soon as the righting is com- 

 plete, the animal is turned anew on its back. It now tends to 

 rigid itself in the same way as in the previous case. That is, the 

 same rays are attached, the same ones go over ; the turning takes 

 place as before. The impulse determined in the previous reaction 

 persists through the second reaction. 



Thus in this second reaction the direction of turning is not 

 determined by any present external factor whatsoever, but by a 

 persisting internal disposition to turn in a certain way — to use 

 certain rays in certain roles. We shall give further details of 

 this persistence of the impulse in our general discussion of the 

 impulse and its nature (p. 145) ; here we are merely enumerating 

 the factors on which, in different eases, the righting reaction 

 is found empirically to depend. 



(14) Impulse present at the time the animal is turned. — At 



