394 
R. P. COWLES 
These experiments undoubtedly show that the rays react to food 
even as far out as the tip and independently of the mouth or the 
rest of the disc. Furthermore, they indicate that sense organs 
are present either on the tube-feet or on the ambulacral surface 
of the rays, which are sensitive to organic substances in solution 
or suspension and that some of these substances stimulate the 
tube-feet either directly or indirectly in such a manner that ob- 
jects are carried toward the mouth, while others do not. 
METHOD OF RIGHTING 
The method of righting of ophiuroids has been studied by Grave 
(1900), von Uexklill (1904) and Glaser (1907). Grave (p. 87) 
says: ^'Two adjacent arms straighten out so that together they 
form a straight line. On these arms as an axis the body revolves, 
being pushed over by the three remaining arms, but mostly by 
the median one of the three.'' Von Uexkiill (p. 11) finds that 
when Ophioglypha is placed on its aboral surface, the rays become 
bent under so as to raise the disc off the bottom and the weight 
of the disc causes the ophiuroid to topple over into its normal 
position. Glaser (p. 208) recognizes a factor in the mechanics 
of turning which I think is quite important. He says that move- 
ments occur at the bases of the straightened arms and in the inter- 
radial portion of the disc between them whose effect is to start 
the righting. 
In fresh, healthy specimens of Ophiocoma echinata, which 
have not been tired out by experiments and which have been kept 
in pure sea-water, the behavior in righting is as follows: As 
soon as the specimen is placed on its aboral side the tube-feet 
begin to move in all directions, and almost at the same time the 
disc is raised off the bottom by the stiffening and pushing of the 
rays. Then two of the rays spread out much as an acrobat doing 
the split," their distal ends twist over into their normal position 
and the disc begins to turn over. Usually the leverage seems to 
be at the proximal end of the rays near where they are attached 
to the disc {i.e., the two rays forming ''the split"). There seems 
to be a decided twisting as a result of the contraction of certain 
