Reaction to Light and other Points in Behavior of Starfish. 103 



It is certain that many starfish show a decided tendency to cHmb 

 the vertical walls of a small aquarium when exposed to light; it is also 

 true that starfish while climbing a wall are under the influence of the 

 attraction of gravitation ; there is no doubt that in going up a wall they 

 move in an opposite direction to that of the attraction of gravitation; 

 but it does not follow that the behavior in question is caused by "nega- 

 tive geotropism," i.e., by the "action of the force of gravity" (Loeb, 

 1900, p. 71). It does not seem to me that starfish in an aquarium show 

 this decided tendency because of the influence the attraction of gravita- 

 tion has over them, but that the climbing is simply incidental, the result 

 of the surroundings. The explanation of this behavior must be sought in 

 the stimuli received by the starfish before it was placed in the aquarium, 

 in the stimuli received while in the aquarium, and in the physiological 

 state of the animal. These factors together finally result in the " impulse " 

 (Jennings) to move in a determinate direction. // there is light of much 

 intensity coining from a certain direction the impulse will be such that in 

 the majority of cases the starfish will move toward the source. In so doing 

 if in an aquarium it will soon come to the vertical wall. A characteristic 

 of the starfish is that when once the impulse to move in a certain direction 

 is formed, the starfish is quite persistent in its behavior and continues to 

 move in that direction ; so when the creature reaches the wall it ascends owing 

 to the persistence of the impulse strengthened by the continued stimulus pro- 

 duced by the light. ^ 



REACTION TO LIGHT. 



Echinaster crassispina is a starfish which lives on a more or less flat 

 sea-bottom and which does not crawl under stones and attach itself as 

 does Asterias forreri. It lives in the open and is exposed to the sunlight 

 throughout the day. 



We find Echinaster reacting positively to bright light while Asteria 

 reacts negatively. Echinaster is very sensitive to light and, as we shall 

 see, light perception is not confined to the "eye-spots" at the tips of the 

 rays. A large part of the aboral surface at least seems to be sensitive to 

 light stimuli. Not only does Echinaster, as a rule, react positively to 

 intense light, but it is also sensitive to a light of 2 to 3 candle-power, or 

 even to a light of somewhat less intensity when placed in a dark room. 



Light is undoubtedly a very important factor in determining the 

 movements of Echinaster. The dependence of this starfish on light 

 stimuli is shown in its behavior when placed in the dark. The rate of 

 locomotion usually becomes reduced and the tips of the rays turn upward 

 as if in search of the customary light stimulus. Sometimes a specimen 

 is found lying perfectly still on the bottom of an aquarium with all five 

 rays curled upward. Echinaster usually assumes an exceptional attitude 

 in the absence of light or in light of very reduced intensity, just as Asterias 

 forreri does in the presence of bright light. 



^ Jennings (1907) has recognized the persistence in behavior after an impulse 

 is formed in the starfish, and Morgulis (19 10) has recently drawn attention to a 

 neglected factor in the movement of the earthworm, namely, the tendency to move 

 in a straight line and the obstinate maintenance of a path when once assumed. 



