382 R. P. COWLES 



aster spinosus indicate that the factors affecting the behavior 

 were well under control. 



The method of making a test was as follows : The experimenting 

 dish was almost filled with sea water and set as described above 

 in the bottom of the box ; a starfish which had been kept in dark- 

 ness was placed directly in the center of the bottom of the 

 dish so that the tip of one of its rays was about 2.5 cm. from the 

 white wall; the cloth cover with the light coming through its 

 center was then quickly fastened over the top and the starfish 

 allowed to move. After about 20 seconds, a time sufficient for 

 the reaction to take place, the cover was removed, the position 

 of the specimen noted, and the starfish then put back in a dark 

 receptacle. The method of handling the specimen, the position 

 of the white wall with reference to any possible tilting of the bot- 

 tom of the dish, the opening and closing of the cloth cover, the 

 position of the arms and madreporite of the starfish with reference 

 to the white wall, were all varied in the tests so as to eliminate 

 any of these factors in the determination of the direction of 

 movement. 



Echinaster spinosus, unlike the species used by Jennings, 

 tends to move toward the regions of ordinary light intensity 

 and away from darkness. In 200 tests made with 40 specimens 

 of this species, only in 10 cases was it found that the starfish 

 had moved toward a black wall and in these cases it seemed 

 probable from the position of the specimen that it had not moved 

 there directly. This surprisingly uniform reaction was due to 

 the influence of either the white or the black wall. 



What is to be inferred from this behavior ? Does it mean that 

 the starfish has vision ? It seems to me that the behavior is 

 due to the relative illumination of the different parts of the body 

 just as in the case of a starfish moving toward a bright source 

 of light. While in the experiments the lamp was so placed that 

 the walls did not cast what we call shadows, yet those parts of 

 the surface of the starfish near the white wall undoubtedly were 

 more brilliantly illuminated than those near the black wall. 



