FACTORS IX THE BEHAVIOR OF OPHIUROIDS 395 
muscles of the rays which are attached to the somewhat rigid 
skeleton. This twisting starts the turning over of the disc which, 
after a certain point, continues as the result of its own weight, 
drawing the other rays over after it. The tube-feet do not aid 
in the righting nor do the three rays which are drawn over help 
as a usual thing. In fact, often very active specimens seem to 
right themselves without raising up the disc but simply by twist- 
ing the proximal parts of the two rays forming ''the split." It 
must be remembered that Ophiocoma echinata and Ophiocoma 
riisei have comparatively long and heavy rays. 
In order to test the assumption that the twisting of the rays is 
an important point in righting, three of the rays were amputated 
close to the disc of a specimen which was then placed in a dish 
of sea-water with the ambulacral surface uppermost. Almost 
immediately the two remaining rays assumed ''the split" like 
position, the distal ends turned over and the twisting continued 
until the disk was brought into its normal position. This series 
of movements was accomplished with apparently little difficulty 
and the specimen was even successful in righting itself when some 
pressure was apphed to the edge of the inverted disc from which 
the rays were amputated. 
Four rays were removed from another individual, which was 
then inverted and in a similar manner by the twisting of a single 
ray the disc was righted. 
These experiments seem to show quite clearly that the twisting 
of the rays is an important part of the righting of Ophiocoma 
echinata and that the righting can be accomplished by the move- 
ments of the two of the rays without the aid of the other three. 
BEHAVIOR UNDER NATURAL CONDITIONS 
Before discussing the experiments carried on in the laboratory 
to test the behavior toward light and other factors, I shall de- 
scribe some observations made on ophiuroids in their natural 
habitat. One of the best places to find these creatures, in the 
region around Loggerhead Key, is on the western side of a typical 
coral reef lying a short distance off the east side of Bird Key. 
THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 9, NO. 2. 
