400 
R. P. COWLES 
directly to the corner d, with the ray leading that had been in the 
corner at a. 
These two experiments show again in quite a clear manner the 
persistence of the stimulus produced by the contact or breaking 
of the contact of the ray with the corner of the dish. 
The current in the water produced by pushing the ophiuroid 
from one region to another seems to have no effect on the behavior. 
If, for example, we pick up the ophiuroid and carry it out of the 
water to another position in the dish the behavior is the same as 
when the specimen is pushed through the water. An experiment 
was tried in which an ophiuroid was taken from the corner in 
which it was resting (fig. 4, a), and was then carried around the 
room as indicated. It w^as placed at h and immediately began to 
move with the marked ray as director toward its original resting 
place, but finally turned and stopped in the corner c. The be- 
havior here was not quite so characteristic as usual, but the tend- 
ency to use the ray that had been stimulated was evident. Similar 
trials in which the test was less complicated gave much more 
accurate results. 
I have described only a few experiments of over a hundred that 
were tried, and I do not wish to leave the impression that the re- 
sults were always as definite as those mentioned or that there 
were no other factors operating during the experiments; but one 
cannot avoid the conclusion that the stimulus produced by the 
contact or breaking of contact of the ray with a solid wall is a 
very important factor in the behavior of the ophiuroid. The ef- 
fect of this stimulus often persists for some little time, but it may 
easily disappear and in fact be completely dominated by large 
differences in the intensity of light. 
CONTACT STIMULI AND LIGHT STIMULI 
In order to compare the effects of contact stimuli due to solid 
walls and the stimuli due to dimly lighted regions, many series 
of experiments were tried. Their relative value in determining 
the direction of locomotion was tested. 
