Mast, Light Reactions in Loiver Organisms. 



143 



Fig. 10. After LoEr, 1905, p. 27, Fig. 2. 



direct their heads toward the window, move to the edge of the 

 pasteboard and remain at the boundary between the covered and 

 uncovered portions of the tube at A, and especially at the top of 



the test tube. The remarkable thing 



pi ^IT is that they are not distributed evenly 



over the whole brightly illuminated 

 part of the test tube. The explana- 

 tion is as follows: As soon as the 

 animals near the window at B are 

 covered by the pasteboard, the weak 

 rays of light reflected from the walls 

 of the room fall upon them. The 

 animals follow the paths of these rays 

 and arrive at the uncovered portion of 

 the tube" [Italics ours]. 



Experiment -f. — The larvae were 

 found to move to C, toward the win- 

 dow F — F. In the test tube B, 

 shaded as represented in the figure, the light intensity is lower 

 than in the test tube A, not shaded, but the larvae go to C. 



Experiment 5. — The animals move from direct sunlight at A 

 to B into the diff"use day- 

 light. They pass from the 

 direct sunlight into diff^use 

 daylight without even attemp- 

 ting to return into the sun- 

 light. 



In these, as in other experi- 

 ments of LoEB referred to 

 on p. 135, the animals were 

 exposed to light, the ray direc- 

 tion of which must have been 

 exceedingly complicated, 

 since the light was difi^used 

 before it reached the tube 

 in which the animals were. 

 Moreover, the walls of the tube caused still further diff"usion by 

 refraction and reflection. How, then, could it be ascertained in 

 any of these experiments whether the animals moved in the 

 direction of the rays or not } 



s 



Fig. II. After Loeb, 1905, p. 28, Fig. 3. 



