GExXEEAL ADAPTATiUAS 343 



a refined colour-sense. AVliy then should ii have been so highly 

 developed in us? It was one of the finKhmir^ntnl maxims of 

 Darwin that natural selection couhl not prudiK-u absolute, but 

 only relative perfection; and airain, that no species could 

 acquire any faculty beyond its needs. 



The same ar^iments will apply even more strongly in the 

 case of insects. They appear to recognise the colour-, the 

 formSj and the scents of flowers, but we can only vagufly guess 

 at the nature and quality of their actual sensations. Their 

 whole line of descent is so very far removed from that of the 

 birds that it is in the highest degree iinpnjbable that there is 

 any identity even in their lower mental faculties with those 

 of birds. For the colour-sense is mental, not })hysical ; it 

 depends partly on the organ of vision, but more fundamentally 

 on the nature of the nervous tissues which transform the etlects 

 of light-vibrations into the visual impressions which irc rec- 

 ognise as colour, and ultimately on some purely mental faculty. 

 But the colour-sense in insects may be quite other than the 

 bird's or than our own, and mav in most cases be combined 

 with scent, and often with form to produce the recognition 

 of certain objects, which is all they require. 



Yet insects, birds, and the flowers and fruits which attract 

 them, all exhibit to our vision nearlv the same ranjje of the 

 colour-scheme, and a verv similar intensitv, brilliancv, and 

 purity of colour in particular cases; which is highly remark- 

 able if their respective needs were the only etiicient causes in 

 the production of these colours. Looking first at flow( rs, how 

 very common and conspicuous are those of a yelh»w colour, 

 yet far beyond the average are the rich orange petals of tlie 

 Escholtzia and the glistening splendour of st^me of our butter- 

 cups; red and purples are innumerable, yet in the Lobelia 

 fulqens and some other flowers we r(\'ieh an intensity of huo 

 which seem to us un^urpassahly b(\iutiful; blues of the type 

 of the campanulas or the v.'irious blue lillaceir are all in tlieir 

 way charming, but in the blue salvia (Salvia patens) the 

 spring gentian {Geniiana vcrna), and a few others, we perceive 



