REACTIONS TO LIGHT IN PLANARIA MACULATA 93 
that the first tendency to move away from the wounded side is 
probably due to the stimulation of the wound. The absence of 
any movements of this nature in specimens used in the present 
work is most likely due to the fact that no great amount of dam- 
age was done to the surrounding tissues in removing the eye. 
Later, during the process of regeneration, the tendency of the 
animals in Mast’s experiments to move away from the side 
containing the newly regenerated tissue showed, according to 
him, that this newly formed tissue was more sensitive to light 
than the old. The absence of this tendency in the present experi- 
ments may again be due to the small amount of injury to the 
animal during the removal of the eye, and consequently, the 
lack of any large amount of regenerating tissue. 
C. Localized sensory regions in the eye 
1. Extent of localized sensory regions. The experiments of the 
preceding section demonstrate that two opposite reactions may 
follow from the illumination of different regions of the same eye. 
The experiments in this section were designed to outline as ac- 
curately as possible these regions of the eye. 
It will be remembered that the eye of Planaria maculata con- 
sists of a number ofsensory rhabdomes enclosed by an opaque 
pigment-cup: Because of this opaque pigment-cup, the entire 
eye may be illuminated and yet only a portion of the rhabdomes 
will receive this illumination. The area containing the illum- 
inated rhabdomes in any case can be fairly precisely ascertained, 
provided the structure of the eye is known and parallel rays of 
light are used. 
The apparatus used in these experiments was constructed as 
follows: A 125-watt gas-filled lamp was blackened except for 
a small circular area 5 mm. in diameter. A tube about 5 ¢.m. 
in diameter and 45 cm. in length was attached to the lamp over 
the circular area. At equal intervals along the length of the 
tube, three diaphragms containing circular openings 5 mm. in 
diam. were placed. The beam of light thus produced consisted 
largely of parallel rays and was large enough to cover an entire 
eye. The tube with the lamp attached could be shifted to throw 
a beam of light in any direction desired. 
