REACTIONS TO LIGHT IN PLANARIA MACULATA 83 
swer to this, I think, lies in the fact that, while the posierior end 
of the animal is sensitive to light, the anterior end, exclusive of 
the eyes, is more so. 
In regard to the anterior end, regardless of the eyes, being more 
sensitive to light than the posterior, Walter (’07, p.123) says: 
a 
Fig. 8 Camera-lucida tracing of the path in a horizontal beam of light of a 
specimen with both eyes removed. Arrows a and 6 indicate the direction of the 
rays of light. C-H, path of animal. When the animal reached the point P, 
light a was turned off and light b was turned on. At points 7 and 2 the animal 
gave a kind of ‘avoiding reaction.’ This did not occur at 3 and 4. 
Again, when a small beam of sunlight passing through a pinhole in 
an opaque screen was directed locally to different parts of a gliding 
Planaria maculata, it was found that tropic response would occur in 
case one side of the anterior end was illuminated, and that it was not 
necessary for the eye itself to be included in the illuminated area to 
obtain such responses. However, when the middle of the body or the 
posterior end was similarly stimulated the worm could not be made to 
turn. 
