324 On the Colour-patterns of Butterflies. [July, 
of the mucous tunic, and to which many delicate trachez pass 
which distribute themselves throughout them.” 
The wings in an imperfect condition, whilst still enclosed by the 
shell of the chrysalis, are closely folded together with many plica- 
tions. Can any clue to the subsequent arrangement of the colours 
be found in the manner in which the wings are folded in the pupa 
state? Ifa scrawl of any kind be made on paper with a pen, and 
if the paper be folded, the ink being inside and still wet, a sym- 
metrical pattern is produced, the sides of which, like the markings 
on the wings of a butterfly, exactly correspond. And it is manifest 
that under certain conditions of folding, colouring matter of any 
kind might, by a comparatively simple process of arrangement, 
produce patterns remarkable for symmetry and regularity. 
In the limited number of instances in which I have been able 
to examine the sufficiently advanced chrysalis of a butterfly, nothing 
of this kind has been indicated: the like spots on the right and 
left wings do not, in the pupa state, coincide; the folds do not bisect 
the markings; that which becomes a beautifully formed band, begins 
as a mere line, or a shapeless spot; and this stage of the metamor- 
phosis, if watched, conveys a decided impression that the resulting 
colour-pattern is not dependent on the folding of the wings in the 
immature condition. 
The perfect wing of a Lepidopterous insect consists of a delicate 
double membrane, traversed between the folds by nerves or veins 
ramifying from the base. ‘The wings are covered with minute 
scales of various shapes and colours, which, in combination, form a 
pattern much after the manner of the materials used by an artist in 
constructing a piece of mosaic work. 
Three elements then are essential to the wing, the double mem- 
brane, the veins, and the scales covering both. 
The simplest type of colour presents itself in the plain uniform 
tint, exhibited when the scales are all exactly alike. Examples of 
this are rare in nature. A variety of Preris rapz is almost wholly 
white ; Gonepteryx rhamnzi is almost wholly yellow. 
It seems probable, however, that the scales growing on the 
membrane upon or near the veins would be distinguished from the 
scales growing on other parts of the membrane by a freer develop- 
ment of pigmentary matter, and that im this manner would arise a 
kind of primary or fundamental pattern, namely, a pale ground 
with darker lmear markings following the course of the veins, e. g. 
Preris crategt. 
For the present we shall notice only the upper surface of the 
wings, in which the prevalence of the primary pattern is more 
clearly indicated. 
Most butterflies exhibit some traces of the black-veined white 
pattern ; and the pattern itself, with slight modifications, is found 
