276 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
1. All the lights used produced positive responses. 
2. Blue light was the most effective stimulus in the production 
of these responses, and green, yellow and red lights formed a decreas- 
ing series, corresponding roughly to their relative positions in the 
spectrum, the red being but slightly more effective than darkness. 
3. The same sort of reactions were obtained when only the eye, 
or only the skin, was exposed, as when the whole body was exposed. 
50 
65 60 S) 50 45 40 
R ae G 
Fic. 2. Curves representing the relative distribution of effectiveness in the spectrum, 
when the lights are received through both the eye and the skin (— ); through 
the eye only (----); and through the skin only (......). Wave-lengths as 
abscissae, and percentages of positive responses as ordinates. Points marked 
on axis of abscissae are the positions of the wave-lengths of the middle band of 
each light. B = Blue; G = Green; R = Red; Y = Yellow. 
4. After the eye was excised (Table 4), exposing the eye region 
to a narrow beam of light produced practically no positive responses. 
5. Illumination of small areas of skin by a narrow beam of light 
(Table 5) produced positive responses, and the same percentage of 
responses on each of the three areas stimulated. 
OE  ————— 
