VIII 
THE COLOURS OF INSECTS IN GENERAL 167 
pigment in combination with some simple effect of 
structure, and that progressive colour-change, like that 
of Phyllium , may have more relation to structure, eg. 
thickened cuticle, than to pigment. 
Besides the uniform brown and green colours in 
Orthoptera there is not infrequently a development 
of beautiful markings and patterns, especially in 
browns and yellows. Dr. Sharp mentions as a very 
peculiar case that of Corydia petiveriana, where the 
wing-covers are spotted, but not symmetrically. 
In the resting position, however, the two overlap in 
such a way that the markings then appear com¬ 
pletely symmetrical—a case of some theoretical 
interest. 
On the whole there is reason to believe that the 
colours of the Orthoptera are to a considerable extent 
due to lipochrome pigments, whether intrinsic or 
derived is still uncertain. 
In the NeuropTERA, as exemplified by the 
dragon-flies and may-flies, the colours are in large 
part optical. The gauzy wings frequently display 
beautifully changing tints, but in other cases instead 
of being transparent they show graceful patterns and 
markings in shades of brown (eg. species of Myr- 
meleon). The body also often displays bright optical 
colours, especially shades of blue. These colours are 
associated with the development of a considerable 
amount of dark pigment, and are mostly very fugitive. 
Bright coloured pigments are relatively rare, and in 
general terms the colours are due to the dark pig¬ 
ments, or are optical colours produced by the differ¬ 
entiation of the cuticle. The optical colours may 
be associated with a thickening and pigmentation 
