NOTES 



w 

 ' * •* 



THE INFLUENCE OF WHITE AND BLACKBALLS ON 

 THE DIRECTION OF LOCOMOTION OF THE 



STARFISH i 



R. P. COWLES 



(From the Zoological Laboratory, University of the Philippines) 



It has long been known that the starfish has at the end of each 

 arm a little patch of pigment. This is generally spoken of as the 

 ' eyespot " and is considered to be an organ which is sensitive 

 to light, making it possible for the starfish to react to light of 

 different intensities. For example, it has been shown that cer- 

 tain species of starfishes when placed in a box into which light 

 shines at one end only, will almost invariably move toward that 

 end. In this reaction it is probable that the eye-spots are 

 stimulated by the bright light coming from the open end of the 

 box, but it is also true as I have shown (1909) 2 that when the tips 

 of the arms, including the eye-spots, are cut off and the specimen 

 is kept for several days until it has recovered to some extent 

 from the shock, the starfish will still move, though more slowly 

 and hesitatingly, toward the lighted end of the box. 3 This may 

 indicate that the eye-spots aid in directing the movements of 

 the creature, but it also shows that the general surface of the body 

 is sensitive to light. When a very small spot of light is cast 

 upon the upper or lower surface of the starfish, 4 it becomes 

 evident that the integument or the branchiae, and the tube-feet 

 are very sensitive to changes of light intensity. This is further 

 shown by the fact that a small patch of shadow cast upon the 



^he writer is indebted to Professor E. A. Andrews, in charge of the marine labora- 

 tory of Johns Hopkins University at Montego Bay, Jamaica, for the privilege of 

 doing this work. 



2 Year Book of the Carnegie Institution of Washington, No. 8, 1909. 



3 Mangold in a paper which appeared in the same year and possibly before mine 

 found that when the eye-spots were -removed from a star-fish the latter still reacted 

 to light. 



4 The light rays were allowed to pass through several centimeters of water in order 

 to reduce the heat factor to a minimum. 



380 



