110 University of California Publications in Zoology. [Vol. 4 



course little pigmented, and is probably more injured by strong 

 light than is the dorsal surface. 



But when it is possible for the starfish to move so as to de- 

 crease the illumination of the body as a whole, then, as we have 

 before seen, it does so, creeping into a shadow. 



The protection of the tips of the rays from the light seems 

 much less striven for than the protection of the ventral surface. 

 In some cases the starfish comes to rest in the light with ventral 

 surface well protected, but with the tips of the rays so elevated 

 and curved that the eye spots are in the light. After it has been 

 at rest for a time, however, the eye spots are usually so placed as 

 to be protected from the light. 



When the starfish is exposed to a strong light from one side, 

 it commonly moves before coming to rest, as we have seen, away 

 from the source of light. While thus moving, the position of 

 the rays varies much. Often there is no indication of the curv- 

 ing of the rays so as to take the bisynnnetrical form shown in 

 fig. 9. In other cases such a shape is gradually assumed while 

 the movement is in progress. In all cases, so far as observed, the 

 rays are inclined while the movement is taking place, in such a 

 M'ay as to direct the ventral surfaces away from the light. It 

 may be asked whether this is not a mere incidental result of move- 

 ment, the ventral surface being always directed toward the side 

 toward which the animal is moving? Observation shows this not 

 to be the case ; at least if there is any such turning of the ventral 

 surface in a starfish moving when not illuminated from one side, 

 it is hardly noticeable, and is not to be compared to the pro- 

 nounced turning away from the light when the starfish is illumin- 

 ated from one side. 



6. Effect of LigJtt on the Righting Beaction. — This will be dis- 

 cussed in our account of the righting reaction (p. 135). 



7. Vision in the Starfish f — Throughout the reactions to light 

 as thus far described, the effects have apparently been due en- 

 tirely to the relative illumination of different parts of the body. 

 I'he starfish moves in each case toward that part of the body that 

 is least illuminated. 



The question may arise as to whether there exists in the star- 

 fish anything resembling what we speak of as image formation. 



