Reaction to Light and other Points in Behavior of Starfish. 107 



a prism of the solution, thick at one end and thin at the other. A 

 rectangular glass dish lined with dead-black paper and almost filled 

 with sea-water was used for testing the echinasters. This was put with- 

 in the black-lined box and the whole apparatus was then placed so that 

 the direct rays of the sun entered the prism, thus producing a lighted 

 area in the dish which was of graded intensity. 



Four series of tests were made with the sun's rays entering the appa- 

 ratus in the general direction shown in fig. 6. In each series a different 

 starfish was used; two of the specimens were large and two were small; 

 one of the larger ones had all of its eye-spots removed. Without a helio- 

 stat it was impossible to have the light rays enter the apparatus at the 

 same angle in each experiment, but this should make no difference in 

 the results. In one of the four series there were ten tests made ; the angle 

 the sun's rays made with the floor of the apparatus varied in each case 

 as follows: 22°, 24°, 25°, 33°, 44°, 45°, 46°, 47°, 50°, 57°. A test consisted 

 of placing an echinaster in about the middle of the dish of sea-water and 

 of observing its direction of locomotion. In every case the starfish 

 moved apparently without hesitation to the bright end of the graded 

 field and remained there for some time. A series of ten tests with the 

 specimen whose eye-spots had been removed gave similar results, except 

 that the reaction was slower. 



After testing echinaster with the sun's rays entering as shown in 

 fig. 6, the apparatus was turned around so that they entered from the 

 opposite direction. The results were the same as in the test made above ; 

 the starfish moved to the light end of the dish. 



A few tests were made with the sun directly overhead and again 

 in every case the starfish moved to the end most intensely lighted. 



Finally the apparatus was altered so that the layer of ink and water 

 no longer made a prism. The container was set level, so that the layer 

 of water and ink was of uniform thickness throughout. The result was 

 that the sun's rays produced an area of Hght of equal intensity in the 

 experimenting dish. Echinasters tested under these conditions moved 

 about "aimlessly," sometimes in the direction of the rays, sometimes 

 opposite to the direction of the rays, and often from side to side. 



These experiments, it seems to me, make it evident that Echinaster 

 crassispina tends to move from the region of least intensity to that of 

 greater intensity without reference to the direction of the sun's rays. 



There has been an objection raised to the use of a prism containing 

 india-ink particles in suspension. It is claimed that the particles of ink 

 disperse the hght before it reaches the starfish, so that parallel rays do 

 not strike the starfish. Such is undoubtedly the case, for, as Mast (1907) 

 states: "reflection and refraction can not be entirely eliminated, even 

 with the utmost precaution." The writer does not hold that the rays 

 impinging on the surface of the starfish are parallel. Since the rays are 

 not parallel it may be claimed that the particles at the thin end of the 

 prism reflect the rays and that these rays act as a directive influence 

 resulting in movement toward the bright end of the field; but it is also 

 true that the particles at the thick end of the prism disperse the sun's 

 rays and that many of these reflected rays impinging on the surface of 



