80 Univers'ty of California Publications in Zoology. [Vol. 4 



wall, bearing but a single spine, is cut from the remainder, the 

 rosette rises to the top and the pedicellariae open, — this reaction 

 being due to the stimulus of the cut. Now the pedicellariae seize 

 any small object which touches them. Such a piece suspended 

 itself for about a minute by the pedicellariae from the hairs on 

 the back of my hand. 



On the other hand, the large solitary pedicellariae could not 

 be induced to bend over or to open, when isolated on a small 

 piece of the starfish. 



Even in the case of the pedicellariae of the rosettes, of course 

 it will not do to conclude from the possibility of reaction to 

 independent stimuli, that the reactions of each rosette are always 

 due to external stimuli directly affecting that rosette. On the 

 contrary, nothing is clearer than the fact that the stimulus caus- 

 ing the attack is usually transmitted from some other part of the 

 body. The pedicellariae of the rosettes may respond to stimuli 

 far away. A prick on the tip of a ray or the mere touch of a 

 single tube foot from another starfish, often causes all of the 

 rosettes of that ray, and perhaps of one or two of the contiguous 

 rays to rise to the attack. Indeed, a strong stimulation in one 

 region often causes all the rosettes of the starfish to rise, the 

 creature bristling up like an angry cat. 



The large solitary pedicellariae likewise respond to stimuli 

 at a distance, though, as we have seen, at but a short distance. 

 When two of these are near together, a touch on the outer surface) 

 of one commonly causes both to open simultaneously. Sometimes 

 the one touched opens first, then the other. But if one is now 

 stimulated to close by touching the inner surface of the jaw. 

 the other does not close. Thus the stimulus to open is trans- 

 mitted, while that to close is not. 



How is the stimulus for the pedicellariae transmitted to a 

 distance? Von Uexkiill has shown that in the sea urchin this 

 transmission need not pass through the radial nerves, and the 

 same is true for the starfish. If we cut through the radial nerve. 

 or the entire ventral half of the ray, the stimulus is still trans- 

 mitted from one side of the cut to the other. A prick at the tip 

 of this ray may cause the pedicellariae of other rays to rise, or a 

 stimulus on another ray may cause the rosettes of the cut ray to 



