ACTION OF LIGHT.

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have been reared up in darkness, but when matured and transformed intobutterflies they exhibited the usual colours of their species in undiminishedbrilliance. Nay, in the common course of nature, many inseCts pass theirperiod of development in perfect darkness, and then suddenly emerge in thefull splendour of their mature state. This, for instance, is the case with theBuprestids, with the Longicornes, the Curculionides, including the gorgeousdiamond beetle. How, then, can it be contended that the colourationof such species is, in any direct manner, the work of light ? If we found thatthe larva: of brilliant insedts were, as a rule, more exposed to light than thoseof dull and sombre species, or if, when arrived at maturity, the developmentof their colours were at all dependent upon the amount of light which theyencountered, we might then entertain a different opinion.

With artificial colours and dyes the adtion of light is also very doubtful.Let us take the case of rosanilin: it will scarcely be conceded that this dyewas pre-existent in the wood or other vegetable matter from which the coaloriginated. In its subsequent career in the mine, in the gas-works, and inthe colour manufadtory its exposure to light has been trifling indeed. Nor doany fadls seem to indicate that either the quality of the aniline colours wouldbe improved or the yield increased by the adtion of light during the variousstages of its manufadture. We cannot, therefore, pronounce light to beexclusively or pre-eminently the diredt colour-generating force; although that itindirectly promotes the development of colours in organic beings is extremelyprobable.

As a modifier and destroyer of colours the adtion of light is very manifest.Very few colours, natural or artificial, can be long exposed to diredt sunlightwithout undergoing some degree of change, which may vary from a slightalteration of tone to total discharging. Every stage of this adtion maybe seen inthe vegetable world. Certain flowers, such as the wild rose, the blackberry, andnut-blossom, the wood-sorrel and the wood-anemone, are perfedtly bleachedby a few hours’ exposure to sunshine. In other cases there is either a changefrom red to blue or from blue towards red. The former variation can be seenin the flowers of the mountain-heath ( E. cinerea), which when overblown passfrom their original rose to a violet. The second, or inverse, change may beseen in the corolla of many varieties of fuchsia, which is of a blue-violetshade when the flower first opens, but becomes redder and redder the longerit is exposed to the light. The changing colouration of the leaves of trees,as it gradually passes from the pale but bright tones prevalent in spring, tothe full, deep greens of summer, and thence to the maroon, orange, yellow,and brown of autumn, is due in great part to the same agency. This may beproved by a simple and by no means rare phenomenon. When the leaves ofa tree or bush are in their full autumnal colouration, a portion of one mayoften be found which has been doubled and fastened down by some caterpillar.The part thus covered from the light retains its ordinary green hue, whilst allthe rest of the leaf is a maroon or reddish-brown. In the animal world thechanges of colour produced by light are generally destructive. The distinctionbetween fast and fugitive colours prevails, however, here, as well as in theproducts of the' dye-house and print-works. Almost all the colours ofquadrupeds and birds are fast, sustaining indefinite exposure to sunlight with-out modification. Among inseCts the colours of beetles and Iiemiptera are,

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