FACTORS IN THE BEHAVIOR OF OPHIUROIDS 411 
this reason, it would, seem the specimen did not return to its 
original resting place. 
While the contact stimulus received before the ophiuroid is 
inverted surely is a factor in determining the direction of righting, 
the intensity of the light is undoubtedl}'- a more important one. 
It certainly plays an important part in the two experiments just 
described. Both factors are responsible for the behavior observed, 
for when similar trials were made, in Avhich the stimulus of contact 
with the corner walls was such as would tend to make an ophiuroid 
right itself toward the bright light of the window, the creature 
did not, as a rule, right itself in that direction. Such a result is 
shown in fig. 12. An ophiuroid at rest in the position a, with 
two rays against the wall of the dish nearest the window was 
inverted and placed at h. Instead of righting itself toward the 
window as would be expected if the stimulus received from the 
contact with the wall were operating, it righting away from the 
window, using the two rays marked and then moved to the 
position d. 
When, however, as is shown in fig. 13, the side toward the 
window is darkened, with an opaque screen an ophiuroid resting 
at a, when inverted and placed at h, will right itself toward the 
darkened side. 
DIRECTION OF LOCOMOTION WITH INTENSE LIGHT COMING FROM 
ONE DIRECTION 
In all the experiments described above no especial attention was 
paid to the lighting. The ophiuroids were exposed to light rays 
coming from many directions, and although the experimenting 
dish was placed in front of a window, the specimens were not sub- 
jected to great differences in light intensity. As a result, the reac- 
bon to light was not nearly so pronounced as in tests made in a 
box painted dead black inside and open only at one end. Such a 
tox was placed with the open end directed toward the very intense 
light reflected from a bank of white sand; inside of it was put a 
rectangular dish, lined with dead black paper and filled with 
sea-water. Under such conditions when an ophiuroid was placed 
THE JOURNAL OF EXPERIMENTAL ZOOLOGY VOL. 9, NO. 2. 
