296 bulletin: museum of comparative zoology. 



with red. The same reasoning applies to the pairs blue with green, 

 and yellow with red, and explains why there were more positive re- 

 sponses to yellow than to blue in these pairs. In effect green and 

 yellow were the farthest apart of the lights adjacent to each other 

 in the spectrum, as was found to be the case in the reactions to the 

 single lights. 



When we proceed to the consideration of the reactions where only 

 the eyes were exposed to the lights, it is found that the decrease in 

 the responses to the more refrangible light in the several pairs followed 

 pretty closely the order in which the pairs of lights were placed in the 

 Table, that is, there was a more evenly graded series. This was, it 

 will be remembered, also found to be the case in the reactions to single 

 lights. 



The difference in effectiveness between blue and green, when tested 

 in single lights, was only 1 % greater than that between yellow and 

 red; therefore, when blue was paired with yellow, and green with red, 

 there was the same percentage of responses to the green as there was 

 to the blue, though from the relative position in the spectrum of the 

 lights in each of these pairs, we might have expected more responses 

 to the blue than to the green. When blue was paired with green, 

 and 3'ellow with red, there was also the same percentage of responses 

 to the yellow as to the blue. The ineffectiveness of the red light, in 

 the pairs green and red, and yellow and red, of course also had some- 

 thing to do with the equality of responses to the blue and to the green 

 in the pairs blue and yellow, and green and red; and also with the 

 equality of responses to the blue and to the yellow in the pairs blue 

 and green, and yellow and red, respectively. 



When the lights were received through the skin only, there was 

 brought out a greater lack of sensitiveness to differences in wave- 

 lengths, particularly at the more refrangible end of the spectrum, 

 than when the light was received through the eyes only. In the re- 

 actions to single lights, when received through only the skin, there 

 was seen to be less difference in effectiveness between blue and green, 

 green and yellow, and yellow and red, than when the eye alone acted 

 as a receptor. But here, when exposed to balanced lights, this greater 

 lack of sensitiveness on the part of the skin to differences in wave- 

 lengths was seen particularly at the blue end, there being a consider- 

 able difference between the effectiveness of the yellow and the red. 

 The green and yellow also differed markedly in their relative effective- 

 ness, both when paired together, and when paired with blue; though 

 when paired with red, they were very similar, owing to the ineffective- 

 ness of the latter. 



