328 On the Colour-patterns of Butterflies. [July 
which is brownish black. A similar hue on Thecla Quercus is 
formed by scales the colour of a dark cloud. The brightest scales 
on Lycena Phileas are of a watery burnt-sienna hue. Far more 
striking discrepancies between the transmitted and reflected hues of 
scales might be quoted from exotic butterflies: I have selected these 
because the insects are more familiarly known. Viewed as opaque 
objects, even under a moderately high magnifying power, at the 
proper angle the reflected hue comes out superbly, but when the 
light is sent through the scales, a pale, or dull dark tint is all that 
is observable. 
These scales therefore exhibit the phenomena of iridescence, 
and their hues are derived, not from the colouring matter present in 
them, but from striations upon their surfaces; not, however, from 
the strize which under a microscope may be seen on all Lepidop- 
terous scales, but from others far more minute, surpassing, probably, 
in delicacy and uniformity, anything elsewhere to be found in nature. 
The surfaces of iridescent bodies, such as mother-of-pearl and some 
of the ores of iron and copper are often very gorgeously tinted, but 
their hues are mixed and irregular, whereas nothing can exceed the 
purity of colour exhibited by patches of these iridescent scales, 
indicating a wondrous exactness in the intervals between the strie. 
For convenience, I shall call the feature produced in the colour- 
pattern by these iridescent scales, the “ gloss.” 
The gloss seems to have towards the dark vein scales the same 
kind of relation which the blush has towards the pale ground-colour, 
except that it seems to be rather charged upon, than shaded off into, 
the venous scales, being sometimes, as it were, sprinkled or dusted 
upon them, as in Papilio Paris and Teinopalpus imperialis. 
The gloss is rarely seen to form sharply-defined bands or 
patches, nor does it often come in contact with the ground-colour 
or the blush, being almost always surrounded by a black border : 
it frequently suffuses the whole wing,* and is often pierced by the 
black vein scales, which show themselves as spots in the midst of it. 
In rare instances, highly-coloured scales, belonging to the blush, 
exhibit iridescence ; when this occurs the result is exquisitely beau- 
tiful. Thus, in Papilio Vertumnus, a patch of carmine scales on 
the hind-wing is glossed so as to show an amethystine hue when 
seen obliquely; and in one rare species of Ornithoptera the yellow 
patch on the hind-wing has similar reflections. In these butter- 
flies the carmine and yellow hues are the results of corresponding 
pigment granules; the amethystine gloss arising from iridescent 
striz on the surfaces of the scales which contain the pigment grains. 
It is a source of much gratification im all branches of natural 
history, to observe the modifications of an organ through a series of 
* As in some Morphos and many of the Lycxnidz. 
