ARTICLES 75 



The Consideration of Yellow 



Between the number of times that black, white, and brown 

 are used and the number of times the other five colours are 

 found in these insects' wings, there is a wide difference. The 

 five colours green, blue, orange, yellow, and red added together 

 little more than equal white, which is the least of the first three 

 (see diagram No. i). Of the second group, yellow is the most 

 common ; it is found in large areas nearly as often as in small 

 (see diagram No. 2). On referring to diagram No. 7 dealing with 

 the Pierines and Coliines, it is at once apparent that this group 

 of insects accounts for most of the large areas of yellow. The 

 colour is here used in a conspicuous manner, it is centrally 

 placed, and outlined by a band of black just as are large areas 

 of white in the same group of insects. Whether in this case 

 the yellow is conspicuous to the insect's enemies by reason of its 

 colour, will depend upon their colour vision ; however, even if 

 they were colour blind to yellow, nevertheless yellow used in 

 this way must be considered to be conspicuous by reason of its 

 high luminosity. It is noteworthy that in this group the yellow 

 is, as a rule, high in tone. 



Yellow is occasionally used as brown is, in the Satyrinae 

 namely, as a central large area bounded by a marginal pattern. 

 In these cases, the yellow is not high-toned nor of great purity 

 as in the Pierines, but low-toned and muddy. The distribution 

 of small areas of yellow is similar to that of white, but rarely 

 occurs with black to form marginal patterns : they are chiefly 

 found as yellow spots on a dark background, or as a ground on 

 which black or other spots are distributed : such patterns will 

 blend at a distance to form a brown tone with indistinct margins. 

 Thus it is seen that yellow is chiefly used to produce incon- 

 spicuousness, and even in the Pierine group it is doubtful 

 whether colour is a factor in the conspicuous arrangement. 

 It has already been mentioned that green was the third colour 

 to become differentiated visually. There is considerable evid- 

 ence that the other colours were evolved in theTollowing order : 

 yellow, blue, orange, and lastly indigo, which is only seen 

 as a distinct colour by very few people. This has an important 

 bearing on the use of yellow in animal colouration, for even if 

 the majority of animals are not at present colour-blind for 

 yellow, at any rate this colour can have only recently become 



