Introductory Sketch. 23 



continued over the segments which lack spiracles; and it is probably 

 owing to this tendency that the rib-like markings on so many 

 mammals are continued beyond the ribs into the dorsal region. 



Upon these two principles the whole of the colouration of nature 

 seems to depend. But the plan is infinitely modified by natural 

 selection, otherwise the result would have been so patent as to need 

 no elucidation. 



Natural selection acts by suppressing, or developing, structurally 

 distributed colour. So far as our researches have gone, it seems 

 most probable that the fundamental or primitive colouration is 

 arranged in spots. These spots may expand into regular or 

 irregular patches, or run into stripes, of which many cases will be 

 given in the sequel. Now, natural selection may suppress certain 

 spots, or lines, or expand them into wide, uniform masses, or it may 

 suppress some and repeat others. On these simple principles the 

 Avhole scheme of natural colouration can be explained ; and to do 

 this is the object of the following pages. 



Into the origin of the colour sense it is not our province to 

 enlarge ; but, it will reasonably be asked, How are these colours of 

 use to the creature decorated % The admiration of colour, the charm 

 of landscape, is the newest of human developments. Are we, then, 

 to attribute to the lower animals a discriminative power greater 

 than most races of men possess, and, if so, on the theory of evolu- 

 tion, how comes it that man lost those very powers his remote 

 ancestors possessed in so great perfection *? To these questions we 

 will venture to reply. 



Firstly, then, it must be admitted that the higher animals do 

 actually possess this power ; and no one will ever doubt it if he 

 watches a common hedge-sparrow hunting for caterpillars. To see 

 this bird carefully seeking the green species in a garden, and 

 deliberately avoiding the multitudes of highly coloured but nauseous 

 larvae on the currant bushes, arduously examining every leaf and 

 twig for the protected brown and green larvse which the keen eye 

 of the naturalist detects only by close observation ; hardly deigning 

 to look at the speckled beauties that are feeding in decorated safety 

 before his eyes, while his callow brood are clamouring for food — to 

 see this is to be assured for ever that birds can, and do, discriminate 

 colour perfectly. What is true of birds can be shown to be true of 

 other and lower types ; and this leads us to a very important 

 conclusion — that colouration has been developed with the evolution 



