has the upper surface of a dull brown, rests with the wings expanded. As, however, the concealed under surface is not brightly coloured, it is difficult to believe that these different postures and conspicuously different colours can have been brought into existence solely by the action of Natural Selection, which, it is generally contended, has brought about the extinction of those individuals which neglected, when resting, and therefore liable to be “caught napping,” to conceal their arresting colours. There is, indeed, no apparent reason why the female, which has nothing to conceal, should depart from the custom common to Butterflies, of resting with the wings closed and raised, this position effectively protecting the male. The facts seem to show that the coloration of the exposed surfaces of the wings is determined primarily by some physiological factor rather than by the incidence of Natural Selection directly through external agencies. Thus, for example, the action of light on the surface of the wings when in the resting posture may well inhibit the production of vivid pigment owing to some inherent physiological idiosyncrasy. But any individuals which lack this inhibiting factor—as some species which, though resting, are brightly coloured, appear to do—will be eliminated, if they live in an environment harbouring eliminating factors, which the exceptions to the rule we must suppose do not. But on this interpretation the fundamental factor in the determination of the coloration is the action of light. Selection imposes a bar only to certain types of coloration. Some Butterflies and Moths, it has just been hinted, when resting exhibit bright colours. Our “Swallow-tail” the under surface of the wings is as brightly tinted as the upper. Among the Moths may be cited many of the gorgeous Atlas Moths, the Hawk Moths, the beautiful Indian _Dysphania 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 Syntomidæ. 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.