90 W. H. TALIAFERRO 
side was illuminated, viz., after hight 9 was turned on, the animal, 
in consequence of a wandering reflex, turned toward the light; 
but, in this case, instead of describing a circular path away from 
the light, the animal oriented by turning toward the side con- 
taining the eye (fig. 9,9 and W). The rate of movement seem 
to determine which of these two reactions follows when such 
specimens orient by means of the wandering reflex. This will 
be taken up later in greater detail. In the two remaining cases 
in which the animal was illuminated on the ‘blind’ side, viz., 
after lights 5 and 7 were turned on, the animal proceeded at right 
angles to the light until it gave the twisting reflex (fig. 9, 5 and 
7, T). During this reaction the anterior end was twisted and 
directed toward the light in such a manner that the light entered 
the remaining eye. In consequence of this, the animal oriented 
accurately by turning directly away from the light. 
The above observations clearly indicate that when a specimen 
is illuminated on the ‘blind’ side, it does not orient until it moves 
in such a manner as to allow the light to enter the remaining 
eye. When this occurs the specimen orients quickly and accu- 
rately. The mechanism of orientation in such a specimen can 
best be explained by means of diagrams (fig. 10). If, as the 
animal is illuminated on the ‘blind’ side and is proceeding at 
right angles to the rays of light (fig. 10, A, /), it gives a wandering 
reflex toward the ‘blind’ side (fig. 10, A, 2) to such an extent that 
the rays of light enter the posterior region of the pigment-cup, 
the animal turns sharply (fig. 10, A, 3 and 4) toward the normal 
side instead of away from it as it ordinarily does. In rapidly 
moving specimens this reaction is often modified. If the animal 
is moving rapidly, it is often carried around so far that the light 
strikes the rhabdomes of the center of the fundus of the pigment- 
cup apparently before it has had time to react to the illumination 
of the rhabdomes of the posterior edge of the cup. If this hap- 
pens, the animal turns away from the stimulated side instead of 
toward it as in the former case. In other words, it continues 
to turn toward the ‘blind’ side until it is oriented. This reaction 
results in a small circle in the path (fig. 10, A, 2, 3’—6’). A 
third method of orienting to the rays of light, when the animal 
