The Reactions of Planarians to Light 



53 



Fig. I shows a diagrammatic vertical section of this apparatus. 

 The light {A), an incandescent electric lamp, was mounted in a 

 black sheet-iron hood (B) to prevent the escape of any lateral 

 light. This hood was suspended from the ceiling of the dark 

 room where the experiments were carried on and was arranged so 

 that it could be easily raised or lowered, thus changing the height 

 and consequently the intensity of the light with reference to any 

 fixed point below. In the hood, beneath the light, was supported 



Fig. i A, light; B, walls of hood; C, heat screen; DD, diaphragm; E, roof of hood; F, plate-glass 

 floor of aquarium; G, paraffine wall of aquarium; HH, diaphragm to cut off light reflections from 

 paraffine wall; J, wall of reflector box; J, open side of reflector box; K, mirror; L, walls of tunnel; 

 MM, black draperies; N, table. 



a flat-bottomed, clear-glass dish (C) containing distilled water to 

 a depth of about three centimeters. The heat screen thus obtained 

 effectually filtered out the heat rays, allowing only the light rays 

 to pass through. A few inches under the heat screen was inserted 

 a diaphragm (D), painted black, the purpose of which was to aid 

 in cutting out side reflections besides allowing only a central col- 

 umn of light to escape below. A black sheet-iron roof (E) con- 



