FACTORS IN THE BEHAVIOR OF OPHIUROIDS 389 
ity in reaction. Preyer, Romanes, Ewart and von Uexkull 
speak of it, and Glaser looks upon the ophiuroid as ''versatile." 
Bohn, whose paper on the reactions of starfishes and ophiuroids 
appeared shortly after that of Jennings on the starfish, recog- 
nizes variability in reaction and the influence of physiological 
states; he believes, however, and rightly, too, that certain external 
stimuli may be so strong as to annihilate any manifestations of 
internal states. 
It is the purpose of this paper to record some observations made 
on ophiuroids under natural conditions and to describe some 
experiments undertaken in the laboratory to test the influence 
on movement, of light stimuh and stimuli produced by contact 
with solid walls. Incidentally, some observations and experi- 
ments are included dealing with the climbing of vertical walls 
and with the reactions to food. While many of the experiments 
made to test the effect of light and contact stimuli are of such 
a character as to produce considerable uniformity in the reaction 
to a given stimulus, and while it has been the writer's purpose to 
show the rather definite influence of these stimuli, yet every experi- 
ment and every observation has indicated that the behavior of 
the ophiuroid is not stereotyped. At times, when an ophiuroid 
is subjected to a great difl'erence in light intensity, the reaction 
seems to the casual observer to be stereotyped ; but this is not the 
case, for every now and then the behavior is such as to upset all 
calculations on the part of the observer. Given a certain definite 
external stimulus acting on an ophiuroid, one cannot always 
predict the resulting behavior correctly. 
Several species of brittle-stars are quite abundant among the 
coral reefs and coral rocks in the region surrounding Loggerhead 
Key, Florida, and the clearness of the sea-water makes it easily 
possible to observe these animals in their natural habitat. The 
well- equipped marine laboratory of the Carnegie Institution, 
with its large aquaria and ''live cars," affords the investigator an 
excellent opportunity to experiment with them. 
There are seven or eight species of brittle-stars which are com- 
monly found about Loggerhead Key. Of these, the large Ophio- 
coma riisei was used as a rule in the following experiments, 
