1907] 



Jennings. — Behavior of the Starfish. 



103 



Movement away from the Light. — For many purposes the 

 starfish was observed in round glass vessels placed on a table near 

 a window. Under these conditions it is observed that the star- 

 fish, when not distracted by other sources of stimuli, moves di- 

 rectly away from the window, to the opposite side of the vessel. 

 It may thus move with any ray or any interradius in advance. 



Fig. 8.- — Diagram of the different positions of the screen in the experi- 

 ments described in the text. The light is supposed to come from the right. 

 The starfish is at s. 



It was suggested to me by one of the investigators in the 

 laboratory that the light was reflected in a concentrated condition 

 from the concave inner surface of the side of the vessel away 

 from the window, and that this reflection formed the main source 

 of light for the starfish. The animal would then be moving to- 

 ward the strongest light, and would be really reacting positively 

 instead of negatively. This was tested in several ways. (1) The 

 inner surface of the vessel was covered with black cloth, save on 

 the side next to the window, so that there would be little reflection. 

 The starfish moved away from the window as before. (2) A 

 black screen was placed behind the starfish. — on the side away 

 from the light. This screen was placed sometimes perpendicu- 

 larly, sometimes inclined toward the starfish, sometimes inclined 

 away from it (fig. 8). When the screen is inclined away from 

 the starfish (6) such reflected rays as exist are, of course, directed 

 upward into the air, and not toward the starfish at all. When 

 the screen is inclined toward the starfish (c), a dark pocket is 

 formed in the back of the vessel, into which the starfish is moving. 

 In all these cases it moves as readily as before, away from the 

 window or other source of light. There can then be no doubt 

 but that the reaction is really a negative one ; this species of 

 Aster ids tends to move awav from the side from which the liaht 



comes. 



