Reaction to Light and other Points in Behavior of Starfish. 109 



to any change in the stnnulus produced by light. Such behavior, it 

 seems to me, should be explained by the persistence of the "coordinated 

 impulse" (Jennings, 1907). The starfish had been placed in the lighted 

 field ; some stimulus (either the light or other external or internal stimuli) 

 so affected the creature that the tube feet began to move coordinately, 

 resulting in locomotion with a certain ray of interradius directed for- 

 ward; the asterina moved in a definite direction, namely, away from the 

 light; when this impulse was firmly estabhshed and the starfish was 

 moving away from the brightly hghted region it was turned through 180° ; 

 the established impulse to move with a certain ray or interradius forward 

 persisted and the starfish then moved toward the Hght. 



Although T have offered this interpretation of Bohn's experiment, I 

 do not wish to leave the impression that a starfish may not change its 

 sign of reaction to light, as a result, for example, of being subjected to 

 intense light or to darkness for a considerable time. While I believe 

 that the behavior of the starfish with reference to light is largely a matter 

 of the intensity to which it has been accustomed, I have not tried any 

 experiments along this fine. 



EFFECT OF LIGHT RAYS OF DIFFERENT QUALITIES ON THE 

 REACTION TO LIGHT. 



Several investigators have attempted to show that some of the 

 lower organisms exhibit a "preference" or "aversion" for light rays of 

 different qualities. It has been held that animals which react positively 

 to light show an "aversion" to the red and a "preference" for the ultra- 

 violet; and that animals which react negatively to light show a "prefer- 

 ence" for the red and an "aversion" for the ultra-violet. It has also 

 been shown that Daphnia, which is decidedly positive in its reaction to 

 light, repeatedly collected in the yellow-green region of the spectrum. 

 On the other hand, Bert (1869), Merejkowsky (1881), and Yerkes (1900) 

 have offered evidence to show that what often appears to be " preference " 

 or "aversion" for rays of different qualities is probably nothing more 

 than a difference in reaction to lights of different intensities. 



Later I hope to take up the quality-intensity problem, but have here 

 simply recorded the sign of reaction to light of different qualities with- 

 out reference to the intensity. 



Color screens were used, and although these were not monochromatic 

 the transmission was tested by photographic methods so that the quality 

 of the Hght used was known exactly. The tests were made in an appa- 

 ratus Hke that shown in fig. 2, except that the open end of the box was 

 closed. In the closed end was cut an opening into which were fitted the 

 various color-screens. Sunlight was used as a source of light. The 

 results obtained were rather meager, showing only that no one kind of 

 ray is necessary to stimulate Echinaster. The following 4 screens cut 

 out: (a) ultra-violet; (6) ultra-violet and violet; (c) violet and blue; 

 id) green, yellow, orange, and red. A series of 10 tests was made with 

 each screen, 17 in all; the orientation and handling were varied. In 

 every series the reaction was decidedly positive, i.e., in nearly every 

 test the starfish moved toward the light without hesitation. 



