-37- 



baok about as quickly as the tube feet become active again. 



Chemioal stimuli # and light (acting on the eye spot) have 



also been seen to affect the loooraotor starfish in a way wholly anal- 



# Romanes 1883 states that all of the under side of the star- 

 fish is sensitive to odor (chemical stimulation) while Pro.uho (1890) 

 localized these receptors in the terminal tube feet of the rays. 



ogous to the above. 



Physiological a^s distinguished from physical orientation. 



I have described above such changes in the direction of a 

 looomotor starfish as involve also changes in the leading ray,- that 

 is the animal may be going in the direction of a certain ray before 

 the change and ia the direction of the opposite rays after change. It 

 is a matter of common observation, however, that crawling starfish 

 sometimes change their orientation by a rotation of the body as a 

 whole without changing the anterior ray. This is a less common method 

 of changing direction, and is said (Bohn 1908) to-be more frequent 

 anng large and stiff specimens than among small active ones. 



Orientation of this kind may be called "physical orienta- 

 tion" to distinguish it from "physiological orientation" which involves 

 a change of the leading ray. 



Physical orientation may involve three f ictore, any one of 

 which may be more or less completely predominant. These are:: (1) 

 Direct orientation of the leading ray or rays to one side: (2) ao 

 celeration of the tube feet of one side of the starfish and a conse- 

 quent swinging of the anterior rays in the opposite direction: (3) 

 the retardation of the tube feet on one side of the starfish and the 

 consequent swinging of the anterior rays toward the same side. 



