The reactions of Planarians to light . mewhat differentcategory, however, than that of the fresh-water planarians, sinceBdelloura is positive to light, while fresh-water flat-worms arenegative. b Abrupt Changes of Light Intensity in Space Several devices were employed to test the behavior of planarianspassing abruptly from an area of one intensity of non-directivelight into another. The most successful device tried was that inwhich two lights of different intensities were mounted overhead The Reactions of Planarians to Light 65 in the hood of the apparatus already described in Fig. 1, themingl
The reactions of Planarians to light . mewhat differentcategory, however, than that of the fresh-water planarians, sinceBdelloura is positive to light, while fresh-water flat-worms arenegative. b Abrupt Changes of Light Intensity in Space Several devices were employed to test the behavior of planarianspassing abruptly from an area of one intensity of non-directivelight into another. The most successful device tried was that inwhich two lights of different intensities were mounted overhead The Reactions of Planarians to Light 65 in the hood of the apparatus already described in Fig. 1, themingling of their rays being prevented by the insertion of a ver-tical diaphragm (Fig. 3, C), which extended from the regionbetween the lights down to the surface of the aquarium. In orderto place the diaphragm in position it was, of course, necessary toremove the heat screen (Fig. 1, C), the presence or absence ofwhich, however, would not have affected the results sought sincethe water in the aquarium itself was nearly 2 cm. deep and thus. Fig. 3 A, stationary light; B, sheet iron walls of hood; C, vertical diaphragm separating the twolights; D, horizontal diaphragm; E, sheet iron roof of hood; F, plate glass aquarium floor; G, paraffmewall of aquarium; HH, diaphragm to shut off reflections from wall of aquarium; I, wall of reflector box;J, open side of box; K, mirror; L, black tunnel; M, black draperies cutting off side light; N, table sup-porting reflector box and end of tunnel; 0, movable light; P, track for movable light; £?, narrow, hori-zontal diaphragm attached at right angles to the lower side of the diaphragm C, in order to preventthe light rays from the two sources of light, A and 0,from overlapping. constituted an efficient heat screen. By keeping the hood sta-tionary and causing one of the lights (Fig. 3, 0) to slide up anddown at will, it was possible to bring about various contrasts of 66 Herbert Eugene Waller intensity in the field below. The complete plan of the ap
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