THE VARIATION OF THE IMAGINES OF THE LEPIDOPTERA. 63 



the main general lines on which the variation of the species will 

 proceed. Butterflies sit with closed wings, hence it is the undersides 

 of butterflies that are then exposed, and, therefore, the undersides 

 take such form, colour and markings, under the influence of natural 

 selection, as will best protect the individual, e.g., the marbled green 

 and white underside of Euchloe cardamines, which rests on umbelli- 

 ferous flowers, the dark undersides and jagged wing margins of the 

 Vanessids, which hybernate in hollow trees, and exactly resemble dead 

 leaves, when at rest. Then there are the "reed" moths, which, be- 

 longing to many different super-families — Noctuides, Liparides, Cram- 

 bides, Tortricides, Tineides, Zeuzerides — sit by day on the reeds, 

 their bodies closely appressed to the reed, their wings folded partly 

 round it, so that each insect represents a gentle swelling of the stem, 

 culminating in an apparent node on the culm, where the insect's head 

 is situated. The colour of all these moths is a very pale wainscot — 

 the tint of a dead or dying reed — with very fine longitudinal striations, 

 agreeing absolutely with the colours and markings of the reed stem. 

 Another large group of moths — chiefly Geometrides — have the habit 

 of resting on tree-trunks, where their general grey hue, marbled 

 with transverse wavy lines, gives them a very close resemblance to the 

 bark on which they rest. Again, in hilly and mountainous districts 

 particularly, a large number of species rest upon the rocks, when their 

 colour usually assimilates closely to that of the rocks upon which they 

 rest, and these, too, are generally covered with transverse wavy lines, 

 which cause them to be very inconspicuous so long as they remain 

 immovable upon their resting-places. Some moths that rest on walls, 

 rocks, or trees, are marked with green and yellow. Such are the 

 species of Polia, Bryophila and Cleora, Larentiaflavicinctata, and others. 

 These, when at rest, are scarcely to be distinguished from the lichens 

 which grow upon the rocks on which they sit. Then there are the 

 green and yellow moths — the Emeralds, Thorns and Sallows — which 

 hide among the leaves of trees, or the lower herbage, and resemble, in 

 hue, dead or living leaves so exactly, that they are scarcely to be 

 detected, whilst those that rest among the roots of grass and low her- 

 bage, generally, are of various shades of grey, or buff, or brown, which 

 make them very inconspicuous near or upon the surface of the ground. 



It is quite clear that, in all these general cases, and in many 

 special ones, natural selection has produced races, particularly well 

 suited in the case of each species to the environment in which it is 

 placed, also that the more conspicuous individuals become a ready prey 

 to enemies, whilst inconspicuous individuals are more often left to 

 carry on the race. 



One of the most interesting special phases of variation exhibited by 

 British Lepidoptera is that of melanism and melanochroism, the former 

 term being applied to those individuals which exhibit a tendency to 

 develop a greater proportion of black in the ground colour than is 

 exhibited by the type, the latter, when the ground colour is intensified, 

 but not in the direction of becoming blacker. The ab. doubledayaria 

 (popularly known as the "Negro") of Amphidasys betularia may be 

 cited as an example of the melanic class. The ab. ochracea (of a deep 

 ochreous or buff tint) of Spilosoma menthastri, which is white in its 

 typical form, is a very good example of those insects which exhibit 

 melanochroic tendencies. These tendencies are noticed to be much 



