EXPERIMENTS ON ECHINODERMS 



67 



vertical o^lass which can be revolved around a hori- 



o 



zontal axis in the aquarium, it will crawl upward 

 whenever the glass is turned. This is not a compen- 

 satory movement produced by the centrifugal force, 

 for during the rotation of the glass the animal re- 



FIG. 19. GEOTROPIC REACTION OK CUCUMARIA CUCUMIS. 



The animals are in a battery jar (a, 6, c, d). It is filled with water and rests on the bridge 

 B B in the aquarium A A. Running water is supplied through the tube g at o. They 

 collect at the highest point (<r, d) of the glass. 



mains quiet, and not until a quarter or half an hour 

 after the rotation does it begin to migrate upward. 

 Neither is the upward migration caused by the light 

 falling in from above. If the animals are placed in 

 an aquarium in which light is allowed to enter only 

 from the side or from below, they will still crawl up- 

 ward on the vertical sides. In a dark room they be- 

 have just as they do in the light. 



One might believe that the need of oxygen determ- 

 ined the upward migration of the Cucumariai to the 



