CHROMATISM 27 



bosses of gneiss with their dark smoothly 

 weathered surfaces, which are such prominent 

 features in the landscape in many parts of the 

 country, often present an uncommon resemblance 

 to the form of the elephant ; and the converse 

 is equally true as may be verified when a herd 

 of elephants is seen against a background of 

 gneiss, the likeness being based upon the posses- 

 sion of a common ground colour superimposed 

 upon a ponderous bulk. 



Gorgeously coloured butterflies and beetles, 

 small flower-haunting birds, such as the humming- 

 birds of the New World and the sun-birds of the 

 Old World, whose plumage reflects a wonderful 

 metallic lustre, larger birds with majestic males, 

 the powerful diurnal birds of prey, and others 

 afford, to the general rule of concealment, 

 exceptions which do not stultify the rule but 

 are explicable on special grounds of adaptation, 

 selection, season, locality, and dominance. 



Butterflies exhibit themselves in their seasonal 

 flights sometimes in vast numbers, but their 

 abundance at certain times only serves to 

 accentuate their absence or rarity at others ; the 

 rapidity with which an immense noon-day swarm 

 can efface itself is marvellous to behold ; while 

 the pupae and even the larvae are often quite 

 concealed by various devices of shape, position, 

 and colour. So with diurnal birds, the nests of 

 the commonest are often very hard to find and 

 rarely seen. 



