ON COLOURS IN NATURE. 101 
The causes of animal colouring are very various. Some 
living creatures have it in themselves, owing to molecular 
arrangements, the particular tint varying, one may conceive, 
according to the position, quantity, and closeness of the 
molecules, but the brightest colours are not, as a rule, bound 
up with the tissues ; sometimes they arise from a phenomenon 
like that by which the soap bubble shows its prismatic hues. 
Then there is the special matter called pigment united with 
the organic substance, as, for example, the brilliant paint 
carmine is the pigment of the cochineal insect, and the red 
colour of blood which may be collected in crystals is separate 
from the other particles to which it is united. 
A great deal has been already stated relative to the 
colour of butterflies in this paper, but I have hitherto omitted 
to notice that a numerous genus of South American butterflies 
(Lthomia) have their wings entirely free from colouring matter 
and any scales whatever, and as transparent as those of flies ; 
another tribe (Hetcera) has also the whole of the wings trans- 
parent, with the exception of a rose-coloured spot close to 
the base of the lower wing, so that the insect has been aptly 
described by Mr. Bates to resemble a wandering rose petal in 
its flight as the transparent part is unnoticed while it is on 
the wing. Others again as the Acreidew of Africa and Mada- 
gascar have the coloured scales over the whole of the surface, 
with the exception of the tips of the upper wings; and as I 
have dwelt on those butterflies which possessed an under 
side as beautiful as, but completely different from, the upper, I 
may now mention that some species of the South American 
genus Lycoree, for example, have on their under side a 
similarity to the upper surface, but at the same time a very 
faint reproduction of its orange, yellow, and tawny tints and 
inarkings, possibly because the under surface possesses a more 
sparse and scanty arrangement of molecules, or because the 
thinness of the wings produces a reflection of the vivid 
hues and markings that grace the other side. 
To resume, not only do butterflies, when rudely and hastily 
caught, leave powder on the hands of their captor; but birds 
like the white cockatoo leave white powder on the hands, and 
an African traveller was astonished on a rainy day at secing 
his hands reddened by the damp plumage of the bird that he 
had killed. When the particles are scattered they scarcely 
influence the tint, but when close together the effect is very 
conspicuous, as, for instance, the abundance of brown pigment 
that may be seen to underlie the skin of a negro after it has 
been raised by a burn, gives rise to his sable colour, Colour 
