ON COLOURS IN NATURE. 93 
American butterfly. Both are lovely, and should be dis- 
played equally in cabinet specimens, but that of the scarlet- 
and-black, which necessarily receives more of the sunlight, is 
the more gorgeous. Some butterflies have dull upper and 
under surfaces equally, others are beautiful on either side ; 
some, dull on the upper, present a strikingly handsome con- 
trast on the lower, while the greater number are far more 
beautiful above than below. But in those instances where 
each side is beautiful the colours and markings of the two 
sides respectively, be it noticed once more, are very different. 
Hence arises the question, Is the sunlight so important, after 
all, if the under surface that does not enjoy so much radiance 
is, although so different from the upper, and perchance not 
so gorgeous, still so beautiful? But the answer is obvious. 
Sunlight is not, for the most part, necessary to the produc- 
tion, but it is to the maintenance of colour in all organic 
beings, although I could exhibit instances from my own col- 
lection of the differences in colour both of the wings and 
body in a certain dragon-fly (Calepteryx ludovisiana), as 
caught after it had newly emerged, from other specimens 
that had been exposed for some days to the light and heat of 
the sun. Intestinal worms and larvee found in the ground or 
in wood are all colourless, as also are certain little beetles in 
the depths of the crevasses of snowy mountains, or the eye- 
less reptiles and fishes inhabiting the waters of subterranean 
caves, in the same way that sea-kale, rhubarb, &c., are 
effectually blanched when growing amid darkness under an 
inverted pot. A gorgeous butterfly is never, it is true, 
brighter in tint than in the hour when it emerges from the 
chrysalis. It does not become brighter by disporting itself 
day after day in the noontide beam (for its colours are 
altogether differently constituted from those of the 
dragon-fly); but what the sun’s rays do for it is this: 
Its first act on reaching the perfect state is to flutter 
towards the light, and to place itself in a position whence 
it can gradually unfurl, expand, and hang its wings down- 
wards, until those wings, by reason of the warmth, gain 
nerve, and are no longer limp, but fully capable of an extended 
flight. Bright sunshine is requisite for the appearance as well 
as the abundance, no less of dragon-flies than of butterflies, if 
not even more so; and it is worth notice to observe what a 
difference a bright hot day makes in the rapidity and wildness 
of flight of a certain butterfly,—our only British swallowtail, 
P. Machaon, in the Cambridgeshire fens. It is also remarkable 
how, if but a transient cloud pass over the sun, the insects, 
