i^07] Jennings. — Behavior of the Starfish. 83 



different modifying- factors thus far mentioned. The readiness 

 to react, the nature of the reaction, and the transmission of stim- 

 ulation, — all these depend in the varying internal physiological 

 conditions of the organisms. We will take up separately the 

 different actions which the pedicellariae perform, mentioning the 

 various factors determining each. 



I. The rising of the rosettes to the attack. This has been 

 shown to depend on : 



1. Foregoing preparatory mechanical stinnili. The rosettes 

 do not rise in i-esponse to the first, nor completely even to the 

 second or third stinuilus. We can distinguish thus a resting con- 

 dition and a series of intermediate preparatory conditions, before 

 the rosette reaches the active condition in which it responds to 

 a weak mechanical stimulus. 



2. Preparatory chemical stinnili induce a condition in which 

 the rosettes rise more readily under the usual mechanical stimuli. 



3. Foregoing chemical stimuli of a certain character have the 

 opposite effect, inducing: a physiological state in M'hich the rosette 

 refuses to attack under the stimuli that usually cause it to do so. 



4. Cutting the radial nerve leaves the rosettes in such a state 

 that they attack more readily than usual in response to any me- 

 chanical stimulation, either close by or at a distance. 



5. Weakness in the animal, from long confinement, causes the 

 rosettes to attack less readily in response to stinnili at a distance 

 from them. 



6. The rising of the rosettes in a certain region leaves them 

 after subsidence in such a state that they react more readily to 

 stimuli in a distant part of the body than do even rosettes nearer 

 the source of stimulation. 



7. There are general differences characteristic of individual 

 starfish. In some all the rosettes attack readily; in others the 

 attack is not easily brought about. 



II. — The opening of the pedicellariae. This depends on the 

 following factors : 



1. Homogeneous preparatory stimuli. In a series of similar 

 stimuli, several are usually required before the pedicellariae 

 respond by opening. There are several variations to be noted 

 here: 



