172 PHYSIOLOGY OF INSECTS. 



and colour of surface : — the variations of form are admit- 

 ted on all hands to be more important than those of colour, 

 for whilst form is generally uniform throughout every indi- 

 vidual of a species, colour is known to undergo a great and 

 almost unaccountable change : in beetles which have wing- 

 cases of a pale brown, with a metallic gloss on them, we 

 shall be sure to find individuals of a brilliantly metallic 

 blue or green, without a trace of brown; and those of 

 which the usual colour is a brilliant metallic green, are 

 sure occasionally to produce varieties of pure black : 

 colour must therefore be taken as a corroborative, rather 

 than a primary character ; it must be carefully noticed, 

 and its changes will often be found of great interest and 

 importance, but it must not be regarded as a positive and 

 definitive character. 



On Colour. — On the subject of colour many vague and 

 crude ideas have prevailed, and much that appears very 

 nonsensical has been written. Latreille is the least theo- 

 retical writer on the subject, and he, for some reason not 

 clearly explained, excludes green fi*om the list of colours. 

 Without however criticising the views of others, the author 

 will, in a few words, explain his own. 



Black in all its varieties appears to proceed from the 

 absence of colour, and can be produced by the exclusion 

 of light : different hues of black may be produced by 

 throwing shade on other colours : a deep shade thrown on 

 blue will produce an indigo ; on red will produce a brown, 

 &c. ; thus blacks and browns originate in nature in a 

 deficiency of light. 



White is the presence of light, and the completeness 

 and perfection of colour ; other colours are subsidiary to 

 it, and component parts requisite to its perfect develop- 

 ment. 



The component parts of white are six, — Red, orange. 



