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vi ORIGIN OF THE COLOUR-SENSE 415appearance ;and this seems quite in accordance with the variousfacts set forth by Mr. Gladstone and the other writersreferred to. The fact that colour-blindness is so prevalenteven now is, however, an indication that the fully-developedcolour-sense is not of primary importance to man. If it hadbeen so, natural selection would long ago have eliminated thedisease itself, and its tendency to recur would hardly be sostrong as it appears to be.Concluding Remarks on the Colour-senseThe preceding considerations enable us to comprehendboth why a perception of difference of colour has becomedeveloped in the higher animals, and alsowhy colours requireto be presented or combined in varying proportions in orderto be agreeable to us. But they hardly seem to afford asufficient explanation either of the wonderful contrasts andtotal unlikeness of the sensations produced in us by the chiefprimary colours, or of the exquisite charm and pleasure wederive from colour itself, as distinguished from variouslycolouredobjects, in the case of which association of ideascomes into play. It is hardly conceivable that the materialuses of colour to animals and to ourselves required such verydistinct and powerfully-contrastedsensations ;and it is stillless conceivable that a sense of delight in colour per se shouldhave been necessary for our utilisation of it.The emotions excited by colour and by music alike seemto rise above the level of a world developed on purely utilitarianprinciples.