74 SCIENCE PROGRESS 



In contrast to this use of white is the effect of a black 

 marginal band outlining a coloured object. A white line crossing 

 red and blue backgrounds enclosed on either side with black 

 lines will not appear pale red or blue but will maintain its 

 original whiteness. Similarly the white, yellow, red or other 

 colour of an insect which is outlined with black will not be 

 affected by any background against which it may be viewed. 

 For this reason a black marginal band is a great aid to con- 

 spicuousness, as it isolates the colour of the insect from that 

 of its background. 



White is also sometimes used as a groundwork on which 

 darker patterns of spots and stripes are laid, as in the Parnas- 

 siinae and in some of the Papilioninae. On referring to the 

 Euploeinse, diagram No. 3, it is seen that small white is largely 

 used in this group, but its distribution is unusual : instead of 

 forming a marginal pattern, it is often scattered through the 

 wing in the form of small spots which do not approach the 

 margin. This arrangement will be less conspicuous than a 

 plain wing .but more conspicuous than one in which the pattern 

 is near the margin. As to whether this moderately conspicuous 

 pattern is related to the visual perception of their enemies, 

 cannot here be discussed. In a few cases white is used in 

 moderate amount, chiefly in the form of bars crossing one or 

 both wings ; this condition has not been subjected to experi- 

 mental analysis. Thayer looks upon such marks as concealing 

 by disrupting the insect's outline and form (Thayer, Concealing 

 Colouration in the Animal Kingdom, p. yy). 



Large white forms 12 per cent, of the cases in which white 

 is used. Referring to the diagrams it is seen that the vast 

 majority of these are found in the Pierine group, where thirty- 

 three examples occur. In these insects, the whole wing may 

 be white, but more often it is outlined by a black marginal 

 band, an arrangement which must render the insect very con- 

 spicuous for several reasons: (1) because a light-centred, dark- 

 margined eye-spot pattern results (see p. 72) ; (2) because of a 

 great tone and colour contrast between the natural background 

 and the white of the wing's centre which is protected from 

 diffusion by the black margin ; and (3) because of the great 

 luminosity of the colour white. The factor luminosity is dealt 

 with on pp. 75 and 76. 



