482 



ALFRED O. GROSS 



only slightly by the yellow (figs. 16 and 17). When green and 

 blue are opposed, the course of a larva oriented by two lights is 

 at an angle to the direction of the rays as shown in figure 15. 

 If the course of the larva under the stimulus of these two fights 

 had been at right angles to the rays the potencies of green and 

 blue, so far as this experiment is concerned, would have been 



Figs 15 to 20 Paths traced by Calliphora larvae, in dilute solutions of methyl- 

 ene blue, in response to balanced pairs of monochromatic lights of the following 

 pairs : 

 Fig. 15 Green-blue Fig. 18 Blue-green 



Fig. 16 Green-yellow Fig. 19 Blue-yellow 



Fig. 17 Green-red Fig. 20 Blue-red 



shown to be equal. The larva, however, regardless of the light 

 in which .it was first started was oriented toward the blue in a 

 direction at an angle with the direction of the rays. 



In a similar way figures 18 to 20 show that blue is more effec- 

 tive than yellow or red, but less than green. A larva started 

 in the yellow or red is completely reversed in its course by the 



