76 W. H. TALIAFERRO 
of normal animals to a horizontal beam of light, it was noted that 
animals usually turn directly away from the light without any 
preliminary trial movements. This is certainly true in the ma- 
jority of cases. A study of orientation in different intensities 
of illumination, however, reveals, among other things, that a 
given specimen may even turn first toward the light and then 
away from it. 
If the lateral illumination is of a very low intensity, the animal 
orients by describing a rather broad arc of a circle with barely 
any perceptible bending of the body. If the intensity is some- 
what higher, the animal does not describe this arc, but turns 
its head directly away from the source of stimulation, making a 
rather sharp angle in the contour of its body just posterior to 
the cephalic lobes. As the light intensity is increased, the animal 
still bends its head away, but the angle, i.e., the point of bending, 
becomes situated more and more posteriorly until it reaches the 
region of the pharynx. When the animal bends its body in the 
region of the pharynx, as it does only under the influence of very 
intense light, a peculiar reaction takes place. The specimen 
raises the anterior half of the body and violently turns it, first 
toward the light, then in the opposite direction until it faces 
directly away from the light, after which the head is lowered and 
the animal proceeds as usual. The reaction of turning the head 
first toward the light and then away under the influence of strong 
stimulation will be taken up later. 
In studying the relation between the character of turning 
during orientation and the intensity of the ight, no attempt was 
made to measure accurately the illumination because of the great 
individual variation and the great variation in the same speci- 
men at different times. Then, too, in working continuously 
with a given animal, it becomes more and more indifferent to 
stimulation by light. The following detailed description will 
illustrate the character of the results obtained in all of the the 
numerous observations made. 
On September 7, 1916, a specimen tested two hours after 
collecting described a rather broad arc of a circle in orienting 
in an illumination of 52 meter-candles (fig. 6, 4). When the 
