Reaction to Light and other Points in Behavior of Starfish. 105 



While I suppose it will not be doubted that light has a directive 

 influence on the direction of locomotion of Echinaster, yet it may be well 

 to state that series of tests were made in which the entrance of the light 



Table 



into the apparatus was regulated by black screens. Sometimes the light 

 was only allowed to enter by a A^ertical slit at one comer, sometimes at 

 the other corner, and sometimes in the middle of the open end of the 

 apparatus. As a rule, the starfish moved directly toward the slit irre- 

 spective of the lattei^'s position. 



PARTS SENSITIVE TO LIGHT. 



Tiedemann (1815), who was one of the first to study the starfish, 

 came to the conclusion that the whole surface was sensitive to light. 

 This was before the discovery of the eye-spots in the starfish. After these 

 organs had been found, however, they came to be considered as the light- 

 receiving organs. Both Romanes (1885) and Preyer (1886-1887) con- 

 sider the presence of eye-spots necessary to produce a reaction to light. 

 AA^hile Bohn (1908) does not state that the eye-spots are the only organs 

 sensitive to light in the starfish he studied, yet he does not mention any 

 other parts as being sensitive. Uexkull in his numerous papers has not 

 taken up the reaction of starfishes to light, but his experiments with 

 sea-urchins show that these creatures react to dift'erences in intensity 

 of light, even though they have no eye-spots. 



In order to determine the effect of the removal of the eye-spots on 

 the reactions of Echinaster to light, several individuals were used and 

 each was first tested before the operation in the apparatus shown in 

 figs. 2 and 5. All specimens reacted positively to the light in almost 

 everv test and moved to the Hghted end of the dish. The tips of the 

 rays of these starfish were then cut off about i cm. from the end, so that 

 all the individuals were without eye-spots. The operated starfish were 

 then allowed to recover from the shock under as favorable conditions 

 as possible. Two hours after the amputation the starfish were again 

 tested. The results obtained with one individual are shown below. 



