82 W. H. TALIAFERRO 
The specimen used in this experiment was first tested in a 
horizontal beam of light in which it was found to orient very 
precisely. The animal was then anesthetized with CO, and 
both eyes removed. ‘Twenty-four hours after the operation, the 
animal was again tested and its movements traced with a camera 
lucida. This tracing is reproduced in figure 8. At the beginning 
of the experiment, the animal was laterally illuminated and it 
proceeded for a short distance at right angles to the rays of light 
and then turned directly toward the light. Movement in this 
direction continued for only a short distance, when it turned 
again and proceeded in a diagonal path away from the light. 
This path soon led out of the beam of light into the shadow. 
Twice as the animal attempted to proceed from the shadow back 
into the light it hesitated, and after a sort of ‘avoiding reaction’ 
proceeded back into the shadow (fig. 8, 7 and 2). The third 
time it came to the margin between the light and the shadow it 
passed into the light without any perceptible reaction. The 
direction of the hight was now changed through an angle of 90° 
(fig. 8, P). The animal described a very irregular course away 
from the second light source. While proceeding away from this 
source it again moved from the illuminated region into the 
shadow and vice versa on two separate occasions, with no apparent 
reaction (fig. 8, 3 and 4.). After these observations were made, 
the animal was fixed, sectioned, and stained. A study of these 
sections revealed that the eyes had been entirely removed and 
that there was no apparent injury to the ‘brain’ or other organs. 
If, now, the reactions of this specimen in a horizontal beam of 
light are compared with those of normal specimens in similar 
illumination, it becomes evident that orientation is dependent 
upon the eyes. This conclusion is, moreover, strongly supported 
by the fact that blind specimens again orient precisely after the 
eyes regenerate. 
Although the eyes are clearly functional in orientation, the 
evidence at hand indicates that there is in eyeless specimens at 
times some indication of a slight orientation to the rays of light. 
The question then arises as to what factors are involved in the 
slight tendency toward orientation in these specimens. The an- 
