404 
R. P. COAVLES 
region opposite to its original resting place; that is, apparently 
without reference to the contact stimulus. In other words, the 
stimulus produced by the proximity of a shaded region seemed to 
dominate over the stimulus produced by contact with the corner 
walls. 
The above series of experiments was finally completed by submit- 
ting the ophiuroid to a number of trials similar to those described 
at the beginning of the series. That is, the screens were removed 
from both corners and the specimen was tested in respect to the 
effect of the contact stimulus. Its behavior now became similar 
to that at the beginning of the series. The ophiuroid reacted 
definitely to the stimulus produced by contact or breaking of 
contact with the corner walls of the dish. It must be men- 
tioned, however, that the return to the starting point was not so 
accurate, a fact which may be due to a persisting effect of the 
stimulus of the darkened regions or to fatigue. 
From these experiments we may draw the following conclu- 
sions : Solid walls and darkened regions are important factors in 
the behavior of Ophiocoma riisei, Ophiocoma echinata and Ophiura 
appressa. The stimulus produced by the contact or breaking of 
contact with solid walls, especially a corner, persists for an appre- 
ciable time, long enough so that the ophiuroid will react to the 
stimulus some little time after and will tend to return to the object 
producing it, or more accurately, will tend to move with the ray or 
rays that received the stimulus forward. A region of reduced 
light intensity, such as the dark pocket in the above experiments, 
also acts as a stimulus on these ophiuroids and produces a positive 
reaction. The darkened region seems to have an effect from some 
little distance (several centimeters) a phenomenon observed by 
Jennings (1907) for the starfish and by Bohn (1908) while testing 
the effect of light and dark screens on ophiuroids. This phenom- 
enon will be discussed later. An analysis of the relative value 
of these two factors in the behavior seems to show that the 
stimulus produced by a region of much reduced light intensity 
is more important than the contact stimulus in determining the 
direction of locomotion. However, when these ophiuroids move 
into a darkened region the subsequent behavior is dependent on 
