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R. P. COWLES 
in the dish it ahnost immediately and almost invariably moved to 
the darkened end of the dish. Previous stimuli produced by con- 
tact with solid walls and methods of handling seemed to have no 
effect. The experiment was repeated many times, varying the 
position of the rays with reference to the open end of the box, and 
almost always the reaction was negative to the light. Usually 
after a great many trials the ophiuroids showed signs of fatigue, 
and then might fail to react or even might move in a positive 
direction. However, the tests showed plainly that the ophiuroids 
experimented with as a rule react strongly in a negative manner to 
intense light. 
RIGHTING WHEN EXPOSED TO INTENSE LIGHT FROM ONE 
DIRECTION 
When a normal Ophiocoma riisei is placed with its oral side 
uppermost in the apparatus just described, it rights itself imme- 
diately and quickly. A series of trials made under these con- 
ditions showed that the ophiuroids righted almost invariably 
away from the light. The position of the rays was varied in these 
tests and also the manner of handling, but the behavior in almost 
every case resulted in a righting toward the darker end of the 
dish. While the righting was not always directly away from the 
lighted end, yet it was evident that the impulse was to right away 
from the light. After the specimen had regained its normal atti- 
tude with the oral side down, it moved almost invariably to the 
dark end of the dish. 
It is of considerable interest to compare the behavior of this 
ophiuroid with that of the starfish, Echinaster crassispina. We 
have seen that the ophiuroid reacts negatively to bright light; 
that is, it rights itself away from the source of the light and then 
also, after regaining its normal position, continues to move away 
from the source. On the other hand, Echinaster crassispina, 
which reacts positively to bright light when moving under normal 
conditions, rights itself in the same manner as the ophiuroid, i.e., 
away from the light. So we see the ophiuroid on being inverted 
rights itself away from the light and then continues to move away 
