1^07] Jennings. — Behavior of the Starfish. 81 



rise. Cutting the nerve usually itself acts as a strong stimulus 

 to the rosettes of the region nearby, causing them all to rise 

 and remain extended for some time. Soon after these rosettes 

 near the cut have subsided, a stimulus on some other part of the 

 body caused them to rise quickly; the cut has evidently left 

 them in a condition predisposing to ready reaction. If the nerve 

 is cut in the middle of a ray the rosettes of the distal half seem 

 specially affected, remaining extended for some minutes. 



If the dorsal body wall of a ray is isolated, so that it contains 

 no part of the radial nerve, stimuli on any part of this piece are 

 transmitted to other parts, causing all the pedicellariae to rise. 

 The transmission is not so complete soon after the piece has been 

 cut out, as later. 



Altogether, it is probable that the transmission of stimuli for 

 the pedicellariae takes place in the starfish largely through the 

 nerve nets of the body wall, as von Uexkiill sets forth for the sea 

 urchin. 



It is important not to think of the transmission of the im- 

 pulse to rise as taking place in too simple a manner, or as deter- 

 mined by purely anatomical arrangements. What distant rosettes 

 shall rise w^hen a given point on the body is stimulated depends 

 more on the recent history of the different parts than on the 

 permanent anatomical connections. This is shown by experiments 

 of the following character. In a quiet starfish a certain region 

 (say, the tip of the arm a) is stimulated, till the rosettes of that 

 region rise to the attack. These are allowed to subside, then a few 

 moments later another part of the body, at a distance (say, the 

 tip of the arm d) is stimulated in the same way. Now its pedi- 

 cellariae rise, and also the pedicellariae of the part stimulated 

 before (near the tip of the arm a), though the pedicellariae of 

 the intervening region do not rise. 



Thus the reaction of the rosettes in a certain region leaves 

 them for a time in a changed physiological state, so that they are 

 readier to react to impulses coming from a distance than are even 

 the rosettes nearer the point stimulated. The effective transmis- 

 sion of the stimulus from the arm d to the arm a is not due to 

 any closer nervous connection between these arms than between 

 d and the others. It is due only to the greater readiness of a to 



