294 bulletin: museum of comparative zoology. 



By referring to Table 6 and to Figure 2, in which the positive 

 responses to the different hghts are plotted, it will be seen that the 

 percentage of positive responses in the most effective light was higher 

 when received through the eye alone, than when received through the 

 skin alone. The green light had also a greater effect when received 

 through the eye alone than when received through the skin alone, 

 but the difference between the two receptors was very small. In the 

 yellow light the effect on the eye and the skin was the same, while in 

 the red, the percentage of positive responses was slightly higher for the 

 skin than for the eye. The blue and green, therefore, differed more in 

 effect when received through the eye alone, than when received through 

 the skin alone. The green and yellow, and the yellow and red, also 

 showed this greater difference in effectiveness when received through 

 only the eye, than when received through only the skin, though the 

 differences in effectiveness on the eye were, in these last two cases, not 

 so much greater than those on the skin, as they were in the blue and 

 green. 



The differences in sensitiveness shown by the eye and the skin in 

 the blue and green lights were brought out when both the eye and 

 the skin served as receptors. The blue showed a higher percentage 

 of effectiveness when received through both the eye and the skin, 

 than when received through only one or the other, though this per- 

 centage of effectiveness was not much higher than that obtained 

 when only the eye acted as a receptor. The green showed the same 

 increase in effectiveness when both the eye and the skin served as 

 receptors, but it was considerably higher than when only the eye 

 acted as a receptor. Blue light, therefore, was not so mvich more 

 effective than the green on the eye and the skin together, as it was 

 when the lights were received through the eye only. This decrease 

 in the effectiveness, of blue over green, can probably be explained as 

 follows: the sensitiveness of the eye to blue light was much greater 

 than to green light. The sensitiveness of the skin to blue light was 

 considerably lower than that of the eye, but the sensitiveness of the 

 skin to green light was not much lower than that of the eye. There- 

 fore, when the light was received through both these receptors, the 

 effectiveness of blue light over that of green was considerably de- 

 creased. In both the yellow and the red, the percentage of positive 

 responses, when both the eye and the skin were exposed, was very 

 close to that obtained when only the one or the other was exposed. 

 Since green light was more effective when received through both the 

 eye and the skin than when received through only the eye, there was 



