96 University of California Publications in Zoology. [Vol. 4 



perienced. They subject it to all possible different conditions 

 found in this region. If now it reacts in an adaptive way to the 

 conditions met. remaining- in or following- up those conditions 

 that assist its life proce&ses, and withdrawing from those that do 

 not, then its movements will be of great help to it. How far does 

 it do this? 



Ada-ptiveness of the Movements. — It requires, of course, only 

 most casual observation to perceive that the starfish does do this 

 in at least a large degree. It withdraws from all sorts of things 

 that injure it, — injurious mechanical stimuli, heat, all sorts of 

 harmful chemicals, fresh water, air, obstacles, etc., etc. It is 

 evident that its movements are on the whole adaptive in a high 

 degree ; that if the starfish did not thus withdraw from injurious 

 things it would, under the conditions arranged by the experi- 

 menter, quickly be destroyed. 



While the starfish thus avoids most injurious things, it is 

 equally clear that it follows up conditions that are beneficial to 

 it. It follows food, either when it comes in contact with it, or is 

 reached by chemical stimuli from it (see the numerous interest- 

 ing experiments of Romanes and Preyer on this matter). I have 

 already given, in the account of the food reactions, descriptions 

 of the following up of food by the starfish (see pages 86 and 

 93). If placed between heat and a moderate temperature, be- 

 tween air and the water, between a crushing weight and freedom, 

 the animal moves toward the condition that is favorable to its 

 life processes. How living things happen to possess this extra- 

 ordinary property of selecting those things which aid the life 

 processes is perhaps the deepest question of behavior. 



In the followiug we wish to study in some detail what condi- 

 tions are rejected, what followed up, and how these movements 

 are brought about in the starfish. Some most erroneous ideas 

 have taken root of late in regard to this matter. 



Current Erroneous Explanation of the Negative Beaction. — 

 The fact that the starfish moves away when one of its rays is 

 pinched or otherwise subjected to an intense stimulus has been 

 explained very simply as follows : 



"Romanes found that when one arm of a starfish is stimu- 

 lated, the animal moves in a direction opposite to the stinnilated 



