THE USES OF COLOUR 13 



light, but they cannot be said to possess these colours 

 in their normal position, buried beneath the opaque 

 surface of an animal. 



The existence of non- significant colours is, never- 

 theless, most important, for they form the material 

 out of which natural or sexual selection can create 

 significant colours. Thus, the colour of blood may be 

 made use of for * complexion,' while fat may be em- 

 ployed to produce white markings, as in certain insect 

 larvae. The yellow, brown, and red fatt^ matters of 

 the connective tissue are accumulated beneath the 

 skin in patches, so as to produce patterns. 



All colour originally non-significant 



All animal colour must have been originally non- 

 significant, for although selective agencies have found 

 manifold uses for colour, this fact can never have 

 accounted for its first appearance. It has, however, 

 been shown that this first appearance presents no 

 difiiculty, for colour is always liable to occur as an 

 incidental result. This is even true of the various 

 substances which seem to be specially set apart for the 

 production of colour in animals ; for pigments occur 

 abundantly in the internal organs and tissues of many 

 forms. The brilliant colours of some of the lower 

 organisms are probably also non-significant. In all 

 higher animals, however, the colours on the surface 

 of the body have been significant for a vast period of 

 time, so that their amount, their arrangement in 



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