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 from 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, 



