vm THE COLOURS OF INSECTS IN GENERAL 175 



known as cases of protective mimicry. Again, when 

 such variations arise in the course of experiments on 

 the rearing of larvae, many would regard them as 

 directly produced by variations in temperature. The 

 fact that a British species may be yellow, orange, 

 or red suggests that the pigment produced depends 

 upon the chemical condition of the cells, and that 

 this may be only indirectly influenced by the state 

 of the temperature. There can at least be no doubt 

 that such variations are of much importance in 

 considering the bearing of the colours of Lepidoptera 

 upon the general problems of evolution. 



Mr. Bateson also mentions interesting cases of 

 variations from red to blue or from blue to red in 

 insects, e.g. in the wings of butterflies and the tibiae 

 of locusts. This is especially interesting because 

 blue in insects seems to be always (?) an optical 

 colour, so that the variation in this case must be 

 associated with the development or suppression of 

 surface sculpturing. It is somewhat curious to note 

 that in the same paragraph Mr. Bateson gives as other 

 examples of alternations between blue and red that of 

 various Copepods and of flowers, e.g. pimpernel, in both 

 these cases the colours are produced by pigments, 

 which exist in red and blue forms (see pp. 68, 126). 



2. Artificially produced. — Another question which 

 has attracted much interest in insects is the relation 

 existing between the normal colours of insects 

 showing much variation of tint, and the colours 

 which may be produced by subjecting the developing 

 organism to varying environmental conditions. The 

 subject has of course been especially discussed in the 

 case of the Lepidoptera, and although the whole 



