392 
R. P. COWLES 
could any mucous glands be seen in their tissues. While there are 
no definite suckers present, it is undoubtedly true that a tem- 
porary sucker is formed when the foot presses iteslf against the 
glass. 
It is not only when the ophiuroid is held against the side of the 
aquarium that it adheres, for it often does so of its own accord, 
climbing up almost to the surface of the water. This occurs 
usually when there are no rocks or crevices for shelter at the bot- 
tom of the aquarium. I have observed similar behavior in the 
case of Ophiocoma echinata. Ophiura appressa will also adhere 
if it is held for a time against the glass but neither of these two 
species is so well adapted in this direction as Ophiocoma riisei. 
It might be claimed that the ophiuroids which climb the sides 
of the aquarium are ''positively phototactic" or ' positively 
photopathic," but this can hardly be true because the ophiuroids 
are well known for their tendency to move into places where the 
light is very dim. We might also say that they are "negatively 
geotropic;" but if we mean by this that they are compelled to 
move up the sides of the aquarium on account of the stimulus 
produced by the attraction of gravitation, T do not believe that w^e 
have used the correct term. On the contrary, I believe that 
Ophiocoma riisei as the result of certain stimuli such as difTer- 
ence in light intensity or unfavorable conditions either external 
or internal, forms the impulse to move in a certain direction; 
having reached the wall of the aquarium it will continue mov- 
ing forward and in so doing mount the wall unless the condi- 
tions of contact alter the impulse when it may crawl along the 
base of the wall. 
TUBE-FEET AS FEEDING ORGANS 
Ophiocoma riisei sometimes takes its food as von Uexklill (1904) 
describes ; that is, by a twisting of the arm which progresses from 
the point at which the food particle touches the tube-feet to the 
region of the mouth, but in most cases the food particle {e.g., 
piece of fresh fish) is taken by the tube-feet and carried along by 
them until it reaches the mouth. 
