274 A. S. PEARSE. 



surface. The righting reaction is one of the most characteristic 

 activities of this species. If an individual is placed in a flat- 

 bottomed dish containing sea water and held with its ventral side 

 uppermost until the tube-feet have attached themselves (usually 

 about half a minute), it slowly pulls the body over with the tube- 

 feet until the ventral surface is against the bottom of the dish. 

 The tube-feet are helped to perform this righting reaction by the 

 rings of muscular constriction which pass slowly from one end 

 of the body to the other. The direction of the turning is deter- 

 mined by various factors, light being an important one. For ex- 

 ample, when an individual rests on its dorsal surface with the 

 long axis of the body at right angles to the direction of the light, 

 the ventral surface is usually turned away from the light as the 

 body is righted. 



In order to test the locomotor reactions on an inclined surface 

 four individuals were each given four consecutive trials in the 



h 



I 



Fig. 5. Diagram showing the position in which individuals were placed in the 

 dish during experiments to test the locomotion on an inclined surface. The arrows 

 represent the direction of the light, a, anterior end ; k, high side of dish ; /, low 

 side of dish ; /, posterior end. 



bottom of a round glass dish, which measured thirty centimeters 

 in diameter and contained sea water. This dish was placed directly 

 in front of a window which was the only source of light in the room 

 and the bottom was tipped 5.6° from the horizontal at right angles 

 to the direction of the light rays. Animals were placed separately 

 in this dish with the long axis of the body parallel to rays of light 

 (F'g- 5)- They were first given two trials with the bottom of the dish 



