ARTICLES 77 



spicuously may possibly be accounted for by its late appearance 

 in the evolution of colour vision. 



The Consideration of Red 



Red is the next colour in order of frequency and it occurs 

 almost entirely in small areas (96 per cent.) (see diagram No. 2). 

 In the groups dealt with in detail it only occurs once as a large 

 area, in Tachyris galba ; in this insect both wings are coloured 

 almost entirely red, not a very pure red, but one bordering upon 

 orange. In the text, mention is made that this rare insect is by 

 no means conspicuous in nature and matches in colour the local 

 fallen leaves (Moore, Lepidoptera Indica, vol. viii. p. 16). 



Small red is rarely found except in the Papilionidae, where it 

 occurs eight times in the Parnassiinae, once in the Thaidinae, 

 and thirty-nine times in the Papilioninae. In the Parnassiinae 

 it is the form of eye-spots ; in the Papilioninae as semi-lunar 

 spots or black-centre eye-spots upon the hindwing, sometimes 

 also there is a small spot of red on the forewing close to the 

 insect's body. It is noteworthy that these red marks occur 

 mostly in positions which have been shown to be of little value 

 as sights for pattern in the production of inconspicuousness, 

 namely towards the centre of the wings as in the Parnassiinae, 

 and along the inner margin of the hindwing or close to the 

 insect's body as in such species as Sainai protenor, Iliades agenor 

 (several forms), /. polymnestoroides, Charus daksha, and Achillides 

 tamilana. 



Apart from the question of position, there are other reasons 

 why red, even in small areas, must be considered to be a con- 

 spicuous colouration. Firstly because red arose early in the 

 evolution of colour vision, secondly because it is almost never 

 to be seen in natural backgrounds, and lastly because it has great 

 power of penetration ; it is less dulled at distance by the opacity 

 of the atmosphere than other colours. On the other hand, a 

 combination of small areas of red and green would give rise 

 to an inconspicuous appearance, as will be explained in Part II. 

 There is a further condition in which red appears inconspicuous, 

 namely, at very low illuminations : this depends on the Purkinje 

 effect, wherein the maximum visual perception, which at high 

 illuminations is at orange-yellow, at low illuminations is shifted 

 towards the blue. For this reason, red colouration in nocturnal 

 animals will be inconspicuous. Although the Purkinje effect 



