REACTIONS TO LIGHT IN PLANARIA MACULATA 67 
obviated the necessity of providing any vertical illumination for 
the microscope, the horizontal beam of light used in the experi- 
ment being quite sufficient. Had it been necessary to use verti- 
Fig. 1 Diagram of apparatus for observing reactions of Planaria to a hori- 
zontal beam of light. A, aquarium; B, lamp boxes which can be moved toward 
and away from the aquarium; C, position of drawing-board when camera-lucida 
is used; K, double-throw, double-pole knife switch; L, 125-Watt gas-filled lamp; S, 
screen; 7', wires to wall tap; W, distilled water. 
cal illumination, it might have introduced an extraneous factor 
in these experiments. 
The aquaria in which the animals were observed were rectan- 
gular. They were made of plate glass and Kotinsky cement. 
