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, e.g. 

 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 {e.g. 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 



