l^*^"] Jcnnings.—Behavior of the Starfish. 71 



it must be roused and caused to open, the rosette as a rule be- 

 ginning- to rise at the same time. In some cases the pedicellariae 

 will open before the rosette rises, but this is not usual. If we try 

 stroking lightly the outer surface of a pedicellaria in a rosette 

 that has not risen, taking pains not to touch anything else, often 

 the only effect is to cause the pedicellaria to retract, drawing 

 downward without opening, so that it may almost bury itself in 

 the fleshy mass of the rosette. If we repeat the light taps a num- 

 ber of times, the pedicellaria may now turn a little to one side, 

 then, while thus contracted, open a little and snap together again, 

 — all without affecting any of the surrounding pedicellariae. 

 Next it often rises again to the usual level, and opens its jaws. 

 If anything comes between the jaws, they snap and hold tightly. 

 If the taps on the back of the pedicellaria are very light, usually 

 there is no reaction until twelve to twenty taps have been given. 

 If they are a little stronger, or if the pedicellaria is more sensi- 

 tive, four or five taps are enough to cause it to behave in the way 

 just described. 



But usually it is not easy to get a single pedicellaria to react 

 alone. The stimulus is evidently transmitted through the fleshy 

 substance of the rosette, so that after four or five taps the immedi- 

 ately contiguous pedicellariae begin to open, while the one stim- 

 ulated still remains closed. A little later it opens also, and that 

 portion of the rosette usually begins to rise. 



As we have seen, picric acid causes the pedicellariae to open, 

 though the rosette contracts strongly. 



While thus the opening of the pedicellariae may occur before 

 the rising of the rosettes, this is usually not the case. As a rule 

 the rosettes begin to rise, and this is then accompanied or fol- 

 lowed by the opening of the pedicellariae. But the two actions 

 are not necessarily bound together ; the rising of the rosettes may 

 occur without the opening of the jaws. There is often great 

 variation among neighboring rosettes on the same starfish in this 

 respect. When a certain spot is jabbed with a needle, some of 

 the surrounding rosettes merely rise, the pedicellariae not open- 

 ing till there is a new stimulus, while in other rosettes the pedi- 

 cellariae open even before the rosettes rise, and in other cases 

 the rising of the rosettes is succeeded by the opening of the pedi- 



