vi ORIGIN OF THE COLOUR-SENSE 411 



that visual organs might exist which would differentiate what 

 we term colour by delicate gradations of some one charac- 

 teristic neutral tint. Now such a capacity of vision would 

 be simple as compared with that which we actually possess, 

 which, besides distinguishing infinite gradations of the quan- 

 tity of light, distinguishes also, by a totally distinct set of 

 sensations, gradations of quality, as determined by differences 

 of wave-lengths or rate of vibration. At what grade in 

 animal development this new and more complex sense first 

 began to appear we have no means of determining. The 

 fact that the higher vertebrates, and even some insects, dis- 

 tinguish what are to us diversities of colour by no means 

 proves that their sensations of colour bear any resemblance 

 whatever to ours. An insect's capacity to distinguish red 

 from blue or yellow may be (and probably is) due to percep- 

 tions of a totally distinct nature, and quite unaccompanied by 

 any of that sense of enjoyment or even of radical distinctness 

 which pure colours excite in us. Mammalia and birds, whose 

 structure and emotions are so similar to our own, do probably 

 receive somewhat similar impressions of colour ; but we have 

 no evidence to show that they experience pleasurable emotions 

 from colour itself when not associated with the satisfaction of 

 their wants or the gratification of their passions. 



The primary necessity which led to the development of 

 the sense of colour was probably the need of distinguishing 

 objects much alike in form and size, but differing in important 

 properties, such as ripe and unripe, or eatable and poisonous 

 fruits, flowers with honey or without, the sexes of the same 

 or of closely allied species. In most cases the strongest con- 

 trast would be the most useful, especially as the colours of 

 the objects to be distinguished would form but minute spots 

 or points when compared with the broad masses of tint of 

 sky, earth, or foliage against which they would be set. 



Throughout the long epochs in which the sense of sight 

 was being gradually developed in the higher animals, their 

 visual organs would be mainly subjected to two groups of 

 ra ys the green from vegetation, and the blue from the sky. 

 The immense preponderance of these over all other groups of 

 rays would naturally lead the eye to become specially adapted 

 for their perception ; and it is quite possible that at first 



