lyS 



LIGHT AND THE BEHAVIOR OF ORGANISMS 



beams, one from each of two Nernst glowers so situated 

 that the beams crossed at right angles. One of the glowers 

 was stationary and the light from it constant. The other 

 was mounted on a track so that the light from it could be 



Fig. 27. The lines i, 2, etc., in ^, B, C, D, represent courses taken by four 

 different blow-fly lar\'ae in light of 78 ca. m. intensity, n, direction of horizontal 

 rays from single Xernst glower. Orientation is not as accurate as one would ex- 

 pect if light acts constantly as an orienting stimulus in accord with the theories of 

 Sachs, Loeb, and Verworn. See text. 



varied. The paths taken by the larvae under the different 

 conditions are represented in Fig. 28. 



It will be seen by referring to the figure that the larvae 

 can move in a direction leading from any point between the 

 two sources of light just like all the other lower organisms 

 tested under these conditions. Loeb says (1905, p. 61), 



