1907] Jennings.— Beliavior of the Starfish. 101 



errors. This remark applies as well to the study of the behavior 

 of other animals as of the starfish. 



Three Classes of Protective Reactions. — Turning' now to the 

 movements of the starfish under the action of different agents, 

 we find that it has not merely one, but at least three different 

 protective reactions when a certain point on its body is injured. 

 If for example we pinch the tip of a ray of the starfish, the anh 

 mal may, instead of fleeing, shrink down close against the sur- 

 face on which it is lying, and attach itself firmly with its tube 

 feet. It can then be removed only with great difficulty. This is 

 perhaps the commonest reaction of the starfish to any sudden 

 attack, and it is certainly very effective in preventing the attacker 

 from dislodging or carrying the creature away, as I can testify 

 from my own experience. 



The second reaction to an injurious stimulus, usually com- 

 bined with the one just mentioned, is the rising of the rosettes. 

 the opening of the pedicellariae, and their seizure of any object 

 which they can reach. This has been considered. 



The third possible reaction is that of movement away from 

 the side stimulated, in the way described above. 



A given stimulus may cause in one specimen one of these 

 reactions, in another another, or if a given stimulus is repeated, 

 it may first cause one of these reactions and later another. Thus, 

 two starfish were lying side by side. The middle of a ray was 

 pressed with a glass rod, as nearly as possible in the same way on 

 each. One responded by a rising of the rosettes in the ray 

 pressed, and by taking hold firmly of the substratum with all its 

 tube feet. In the second specimen neither of these reactions 

 was given, but the animal began instead to move slowly away. 

 If the pressure was made a little greater, this animal stopped, 

 took hold firmly with its suckers, and attacked with its pedi- 

 cellariae. Two minutes later an equally strong pressure on the 

 same spot caused only a rapid movement away, without attack 

 on the part of the pedicellariae. These examples are typical of 

 the variations to be observed. 



