100 



Papers from the Marine Biological Laboratory at Tortugas. 



FIG. 2. Apparatus used to test the effect of great differ- 

 ences of light intensity on starfishes. A glass experi- 

 menting dish (36X27X7 cm.) lined with dead-black 

 paper is placed, as shown, in a wooden box (soXszX 

 19 cm.) which is painted dead-black inside and open at 

 one end. The glass dish is filled with sea-water and the 

 whole apparatus is so adjusted that intense sunlight is 

 reflected from a white sand bank into the open end of 

 the box. The top of the box can be removed when 

 starfishes are introduced into the dish. 



Several series of experiments were undertaken in order to determine 



the behavior of Echinaster on inclined surfaces in the presence or in the 



absence of light. In these 

 tests a very simple piece of 

 apparatus was used (fig. 2). 

 Before beginning each 

 series the starfish to be used 

 was tested in the apparatus 

 to observe the starfish's re- 

 action to light. The speci- 

 men was placed in the dish 

 of sea-water, care being 

 taken to have the bottom of 

 the dish level. The method 

 of handling and the position 

 of the rays with reference to 

 the open end of the box were 

 varied, but almost always the 

 starfish moved toward the 



light. Rarely the specimen moved to the darker end, but even then it 



soon returned to the bright end of the apparatus. When the same kind of 



tests were made, the apparatus being 



covered with a thick piece of velvet b ^ 



so that no light could enter the open 



end of the box, the starfish behaved 



differently, moving more slowly and 



without reference to any end of the 



apparatus. Every Echinaster and 



every Astropecten experimented with 



showed a decided tendency to react 



positively to bright light. 



After observing the starfish's 



behavior toward light, as described 



above, a false bottom inclined at an 



angle of 10 was placed in the glass dish and so arranged that the base 



of the incline was at the open end of the apparatus (fig. 3). The results 



of these tests are as follows: 



TABLE i. 



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FIG. 3. Vertical section through apparatus 

 shown in fig. 2, with the addition of the 

 false bottom inclined at 10, and the light- 

 tight velvet cover, a, wooden box; b, vel- 

 vet cover; c, glass dish; d, inclined false 

 bottom. 



The starfish, it will be seen, moved to the lightest end of the appa- 

 ratus and in so doing climbed down the incline. In order to observe the 

 behavior without the light stimulus the apparatus was now covered with 

 a thick piece of velvet, so that it was light-tight. The results were as 

 follows: 



