80 THE CAUSES WHICH PROPAGATE 



painting we discover the sentiments of love, rivalry, and fear 

 have been writ in various hues in ages gone, and have become 

 associated with special feeling, red and white betraying the 

 tenderest natures, and yellows and metallic blues acute light 

 sensitiveness. Indeed, the colouring and patterns of insects 

 may be broadly regarded as a design for mutual attraction 

 of the kinds and sexes subservient to reproduction, or as a 

 means of affording protection to the species; and as regards 

 the individuals, it becomes an expression of pleasure or pain, 

 a language, as I hope to indicate, to shield the various forms 

 for a period against that extinction which has removed suc- 

 cessive eons of geologic life from our terraqueous surface. 

 Nature likewise imparts virtual permanency, by imbuing each 

 more or less Avith the hues and shapes of the evanescent objects 

 where they resort, and thus we commonly find an insect tinted 

 and marked according to the various parts of a tree, the lichened 

 twigs, mossy trunk, spring verdure, or brown horror of autumn, 

 where we may chance to discover it ; among such harmony, we 

 doubt not, it may alone exist, crawl, or fly during its season of 

 activity, or hide in its lethargic hours. And, in fact, we dis- 

 cover the insensible cutting down of forests, drying of marsh 

 land, and cultivation of heaths yearly affords us evidence of a 

 gradual extinction of species, in measure due to this removal 

 of mimetic shelter, although other causes may combine, such 

 as a simultaneous disappearance of food-j)lants, or other intrinsic 

 circumstances. 



On penetrating further into this presiding phenomenon we 

 begin to recognise it is those surfaces in insects which are adapted 

 for coverings, or exposed in repose, that are especially protected, 

 while the parts they conceal often assume bright and striking 

 hues. Deceptive mossy and licheny tints characterise the upper 

 surface of the fore-wings or their representatives in moths, 

 caddis-flies, grasshoppers, bugs, and beetles ; and in the instance 

 of butterflies we notice these appearing beneath and often con- 

 fined to the under-surface of the hinder wings, behind which 

 the primaries may be withdrawn when the wings are shut in 

 repose. Here, however, a South American genus [Ageronia) 

 forms a notable exception. These butterflies rest with their 

 wings flat, and like many moths present superiorly mottled 



