REACTIONS TO LIGHT IN PLANARIA MACULATA 63 
of Mast, the technique employed was very crude. With this 
one exception the method of removing the eyes was to remove 
the entire head. The results of the present paper make it very 
doubtful if conclusions regarding the functions of the eyes can 
be drawn from the study of decapitated specimens. 
The plan of the present paper is, first, to make a careful histo- 
logical and cytological study of the eye in Planaria maculata and, 
second, with this anatomical background, to ascertain, by much 
more precise technique than used previously, the part played 
by the eyes in the reactions to light. This necessitated a study 
of the normal reactions to light. Similarly it led to a study of 
the mechanics of orientation to light in specimens which had 
one or both eyes removed and of specimens having one eye and 
a portion of the other eye removed. It also led to a study of 
the function of the pigment. 
It gives me great pleasure to acknowledge my indebtedness 
to Prof. 8S. O. Mast, under whom the work was done, and to 
Prof. W. A. Kepner, of the University of Virginia, who, besides 
following the work with great interest, tendered many helpful 
suggestions and criticisms. Much valuable assistance was also 
received from Miss M. L. Dinwiddie, of the University of Vir- 
ginia. The author is indebted to Dr. 8. R. Detwiler, of Yale 
University, for the photographs in figure 7 and to Miss B. E. 
Stocking for the drawing in figure 13. 
MATERIALS AND METHODS 
All of the experimental work in this paper was done on a 
planarian found in abundance in an abandoned ice-pond near 
the University of Virginia. Collections were made by bringing 
roots, leaves, and debris from the margin of the pond and placing 
them in large aquaria filled with tap water. In such aquaria 
specimens begin to rise to the top in a few hours. They can 
then readily be removed with a section lifter. Although most 
of the experiments were performed on animals which had been 
freshly collected, it was found that they could be reared in the 
laboratory by keeping them in fresh spring water and feeding 
about once a week with finely teased Tubifex. 
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