294 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
By referring to Table 6 and to Figure 2, in which the positive 
responses to the different lights 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 much 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 
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