480 ALFRED O. GROSS 



the direction of the rays. This pecuharity in the responses of 

 the animals to red Ught as contrasted with their reaction to 

 other balanced pairs of colors indicates that red is less effective 

 in orienting the organism than are the other lights, a conclusion 

 borne out by other lines of experimentation. 



The foregoing experiments, though showing that the larvae 

 are responsive to all the lights and perhaps least effected by the 

 red, do not show the relative potency of the colored lights. To 

 determine this relation, the four monochromatic lights in all 

 their possible combinations were used in testing the responses 

 of the larvae. Typical examples of the records selected to repre- 

 sent the average of the course taken by the larvae under the 

 respective pairs of lights, are shown in figures 9 to 20. Where 

 red was balanced against blue, green or yellow it is evident 

 from an examination of the records (figs. 9 to 11), that red 

 is least effective in orienting the larvae. A larva started in the 

 red is completely reversed in its direction of crawling when 

 opposed by any one of the other lights. On the other hand a 

 path of the same larva started in the blue, green or yellow is 

 only slightly if at all altered in direction by the red light. Similar 

 results are shown in the records of the reactions under the same 

 pairs but with the lights reversed in direction respectively (figs. 

 20, 17, and 14). 



In pairs where yellow is opposed to the other lights, the red 

 is less effective than the yellow in orienting the animal, but the 

 blue and green are more so (figs. 12 to 14). When the larva is 

 started in the yellow it turns sharply and reverses its course at 

 the point where the blue or green is turned on (figs. 12, 13). 

 In these tests where the larvae were started in blue or green 

 several trial movements were frequently made by a larva when 

 it received the stimulus from the yellow light. The subsequent 

 direction of its course in this case is not reversed but it ma}^ be 

 at an angle to the direction of the rays. This experiment shows 

 that yellow when compared with blue and green has an appre- 

 ciable effect on the larvae although it is much less potent than 

 either of these lights. A larva oriented in the red is reversed 

 in its course by the yellow and one started in the yellow is to 



