VIII 
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, eg. 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, eg. 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 
