1^07] Jennings. — Behavior of the Starfish. 107 



Similar behavior is seen when a screen is so placed that its 

 shadow falls across the middle of the body, parallel with the rays 

 of light, so that one-half of the body is shaded, the other in the 

 light. The starfish moves toward that half of the body that is 

 shaded by the screen, — therefore nearly at right angles to the 

 direction of the sun's rays. But the movement is slightly 

 oblique, the path being directed a little toward the side away 

 from the sun. In other words the starfish moves both toward the 

 shadow cast by the screen, and that cast by its own body, the 

 former preponderating in influence. With the same .starfish the 

 screen may be transferred repeatedly from right to left side and 

 back; in each case, after some delay, the starfish changes its di- 

 rection of movement and creeps into the shade. i 



If the screen is so placed as to cover in successive cases less 

 and less of the body, its influence on the movement becomes less ; 

 the path of the starfish forms a smaller and smaller angle with 

 the direction of the rays of light. If less than one-half of the 

 length of the rays of one side is shaded there seems to be little 

 or no effect on the movement ; the starfish creeps directly away 

 from the source of light. 



These results show clearly that the relative intensity of illum- 

 ination on different parts of the body of the starfish may, and 

 does at times, determine the direction of the movement, without 

 regard to the direction of the rays of light. Furthermore, all 

 the experimental results are explicable on this basis, since in a 

 field uniformly lighted from one side the body of the starfish 

 itself serves as a screen to keep a part of its surface unillumin- 

 ated; the animal then moving toward this unilluminated half. 

 The results agree with those of the very careful work of ]\Iast 

 on lower organisms. The thorough work of recent years seems to 

 strengthen the contention of Holt and Lee (1901), that there is 

 little if any positive evidence of the "efficacy of pure direction" 

 of rays of light in determining the movements of organisms. 

 In all cases the results can be equally well understood on the view 

 that the organism tends to move toward the most (or least, as the 

 case may be) illuminated region; and many of the facts admit 

 of no other explanation. 



