402 
R. P. COWLES 
We shall consider only one of these series which is a charac- 
teristic one. In the first place an ophiuroid was submitted to several 
trials such as have been described above and it was found that the 
behavior was as usual. That is, the contact stimulus in the corner 
of the glass dish persisted as a rule and seemed to be the determining 
factor in the specimen's return when, without changing its orienta- 
tion, it was pushed away. Then the corner in which the ophiuroid 
w^as resting was shaded by placing dark screens around it. As one 
would naturally expect, since it is known that ophiuroids react 
positively to dimly lighted regions, the specimen moved in the 
usual manner when put to trial (fig. 5) . That is, after being drawn 
out from the darkened corner, without change of orientation, it 
returned again, with the contact ray directed forward. The 
behavior on reaching its resting place was somewhat different 
from that exhibited in the preceding experiments. The ophiu- 
roid assumed a more settled attitude ; it curled its rays up to some 
extent, thus occupying a smaller space. 
After several trials the conditions were changed (fig. 6) by also 
placing dark screens around the corner, diagonally opposite to 
the one originally shaded. The ophiuroid was then pushed to 
the position h. After some hesitation, undoubtedly due to the 
new shaded region, it moved to c, but without touching the 
corner walls, went to d and finally back to a, assuming its original 
attitude with the same ray in the corner. The behav^ior seemed 
to indicate a conflict between two guiding stimuli; the shaded 
region apparently had an influence, for the specimen changed its 
usual direction of movement and went into the shaded pocket c, 
using the interradius opposite to the contact ray as director. Al- 
most immediately, however, it came out again and moved by 
the way of d to its original resting place with the contact ray lead- 
ing, apparently still under the influence of the contact stimulus 
received at a. 
The experiment just described was repeated seven times, first 
using one shaded corner as the starting point and then the other 
shaded corner. In every case but one the behavior was the same, 
except that the specimen remained in the shaded corner into 
w^hich it had moved (fig. 7). The ophiuroid moved to the shaded 
