SOME OF THE "LOWER ORDERS" 189 



Indian Dys'phania militaris — wherein the whole of the 

 exposed surface is of a beautiful and vivid violet and 

 yellow — and the tropical members of the Burnet Moths, 

 belonging to the family Syntomidae. In all these 

 cases it is not the under but the upper surface of the 

 fore-wings which has thus departed from the usual rule 

 of the tribe. Not the least remarkable feature of these 

 insects is the fact that while the Atlas and Hawk Moths 

 are crepuscular in habits, the Dysphanias and Syntomids 

 and Burnet Moths are diurnal, and revel in the sunlight. 



To revert for a moment to the factors to which these 

 and other bright and often conspicuous hues are due. 

 That all highly-coloured animals are descendants of 

 dull-coloured ancestors there can be no room for doubt. 

 The vivid tints they now display are to be regarded as 

 due to some change in the metabolism, some clarifying 

 process of the organism whereby the various pigments 

 became segregated, concentrated and intensified. But 

 many of the most vivid hues are not due to pigment at all, 

 but to changes in the surface structure of the coloured 

 areas. Such are the wonderful metallic colours which 

 all kinds of animals display. The iridescence is due to 

 the breaking up of the light by reflection from finely- 

 grooved surfaces. 



Whatever their nature, one still asks what is their 

 origin, what brought them into being. They cannot be 

 regarded simply as adaptations which have arisen to 

 meet the demands of the environment, as are the structural 

 peculiarities of the skeleton for example ; for in this case 

 both sexes, and all stages of growth, should display the 

 same hues, and this is rarely the case. Furthermore, 

 we should not in this case be left with a vast assemblage 

 of forms which certainly cannot be " pigeon-holed " as to 



