lOG Papers from the Marine Biological Laboratory at Tortugas. 



The first five of the above tests were made 2 hours after the operation 

 and the balance about 24 hours later. The method of handling and the 

 orientation were varied, but there is every indication that the starfish 

 reacted positively toward the brightly lighted end of the dish. In every 

 test but 2 of the 18, the echinaster moved to the light end. On the second 

 day after the operation the behavior was more direct. There can be no 

 doubt that the eye-spots as well as i centimeter of the ray are not neces- 

 rary in the reaction of Echinaster crassispina to the light. The rest of 

 the surface of the starfish must be sensitive to light (Jennings's work 

 indicates this) to such a degree that the direction of movement is influ- 

 enced by it. In fact, since this work was done I have tested the sensitive- 

 ness of the tube feet and the gills of Pentaccros reticulatus and have 

 found that they react definitely to changes in intensity of light. 



Besides the series of tests recorded in table 8, other series equally 

 convincing were undertaken with different individuals; furthermore, 

 we shall see in some later experiments additional proof that an echinaster 

 without eye-spots is sensitive to light ; while there is no doubt that eye- 

 spots are not necessary, yet it is true that echinasters with these organs 

 removed do not react as quickly as normal individuals. Whether this is 

 the result of the injured condition or the lack of the eye-spots I can not say. 



DIFFERENCE IN INTENSITY OF ILLUMINATION AND RAY DIRECTION 

 AS FACTORS IN DETERMINING THE DIRECTION OF LOCOMOTION. 



So far as I know, Jennings (1907) has been the first to attempt to 

 ascertain whether the direction of the rays of light or the differences in 

 the intensity of illumination on the different parts of the body determine 



the direction of locomotion of the 

 starfish. By manipulating a screen 

 in various ways, so as to cut out 

 the direct action of the sun's rays 

 on the surface of the starfish, 

 Jennings obtained results which 

 point strongly to the view that the 

 "relative intensity of illumina- 

 tion" is the important factor in 

 the determination of the direction 

 of locomotion. 



While many of my experi- 

 ments led me to believe that the 

 starfish {Echinaster) and the brit- 

 tle-star {Ophiocoma\ are influenced 

 more by the relative intensity of illumination of the surface of the animal 

 than by the direction of the rays, yet I undertook the following experi- 

 ments to confirm my belief. A brief preliminary notice of these experi- 

 ments has been published by the writer (1909). The apparatus (fig. 6) 

 described in that paper consisted essentially of a tight wooden box open 

 above and painted dead black inside. Into this opening was fitted a 

 glass container partly filled with water mixed with a little Higgins water- 

 proof ink, so that when the container was in position there was formed 



Fig. 6. — Section through the apparatus used to 

 obtain a field of light of graded intensity, a, 

 light-tight door; b, glass container; c, prism 

 of water mixed with a little Higgins water- 

 proof ink; d, rectangular glass dish containing 

 sea- water and starfish ; e, direction of sun's rays. 



