l^^O'] Jouiiiigs. — Behavior of the Starfish. 73 



The effect of a stimulus when repeated often differs from its 

 first effect. Thus, in many cases I observed that when the gills 

 near one of the large pedicel la riae was struck with a fine rod, the 

 pedicellaria opened slightly, in a weak sort of a way, then closed 

 again. Now the gills were struck again as before; the pedi- 

 cellaria did not open, nor would it open in response to further 

 repetitions of the stimulation. Again, often the pedicellariae 

 will not open in response to one or even several stimuli, but if 

 the stimuli continue, the opening may finally occur. The follow- 

 ing illustrates these variations : Two large pedicellariae, which 

 we may call A and B, stood close together. Each was rubbed 

 lightly on the back of the right jaw, near the tip. Each at once 

 opened about one-eighth of the full amount, remained thus one 

 or two seconds, then closed. Now A was rubbed again in the 

 same way ; it did not open, but instead bent over toward the side 

 stroked. The stinuili were now repeated five times in succession 

 without response, till at the fifth stroke the jaws opened much 

 more widely than before. 



Waiting for two minutes after the jaws of A had again 

 closed, the stimulus was repeated. To the first stroke the pedi- 

 cellaria responded by opening half way ; then after closing it did 

 not respond to the next three strokes, but the fifth again caused 

 it to open slightly. 



In the case of B, the first stimulus on the right jaw caused 

 slight opening. The next three, on the same spot, had no effect. 

 Now the left jaw was similarly stimulated in the corresponding 

 spot ; the pedicellaria at once opened. 



It is evident that the motor apparatus of the pedicellaria is in 

 a state of somewhat uncertain equilibrium, varying at different 

 instants, and depending largely on the recent history of the pedi- 

 cellaria. Its response depends upon its precise state at the mo- 

 ment of stimulation. 



Openii7g of the jaws does not always require a definite stim- 

 ulus. Often, if the jaws, at being opened, are stimulated to 

 close, they at once open again if their first closure did not result 

 in seizing an object. They may of themselves snap repeatedly,— 

 opening and closing without any further stimulus than the pre- 

 ceding- action.— the opening evidently predisposing them to 



