FACTORS IN THE BEHAVIOR OF OPHIUROIDS 413 
from the light, while the starfish Echinaster crassispina under 
similar conditions, also rights itself away from the light, but then 
movies towards the light. In other words, the intense daylight 
coming from one direction produces a negative reaction when it 
strikes the aboral surface of the ophiuroid and also a negative 
reaction when it shines on the oral surface; on the other hand, 
this same intensity of light brings about a positive reaction 
when it stimulates the aboral surface of the starfish, Echinaster, 
and a negative reaction when it stimulates the oral surface. It 
appears then that the same intensity of light acting on the oral and 
aboral surfaces of Echinaster brings about reactions of opposite 
signs. 
INFLUENCE OF VERTICAL DARK AND LIGHT WALLS 
All of the most recent workers in the field of light reactions have 
recognized the importance of the influence of the reflection of light 
rays from various surfaces in the region of the organism experi- 
mented upon. Bohn in some of his earlier papers and in his paper 
on the reaction of starfish (1908), and also Mast (1907) and Cole 
(1907), in their very careful work, have laid special stress on the 
necessity of taking this factor into account. Both Jennings (1907) 
and Bohn (1908) find that the direction of movement of a star- 
fish, which ordinarily reacts negatively to bright light, is influ- 
enced by vertical dark walls even when they cast no shadow; that 
is, these starfish when not too far away from the dark wall will 
react by moving toward it. Bohn also shows that other star- 
fish which react positively to bright light move toward a light 
colored wall rather than a dark one. Another point on which 
Bohn (1908) lays stress is that shadows cast on the horizontal 
surface upon which the starfish lies have but Httle effect in deter- 
mining the behavior of the creatures. While at present I can 
offer no quantitative proof of the correctness of this view for ophiu- 
roids, yet my experiments with hanging dark screens indicate 
that it holds good. 
