VII 
THE COLOURS OF THE LEPIDOPTERA 
155 
table seems on the whole to confirm the idea that a 
relation exists between the two, and therefore that 
the pigments are waste products, but observations on 
colour alone are perhaps not of very great value. 
The dark pigments, as we have already seen, are 
probably identical in all butterflies ; a pure black 
colour is, however, in most cases due to the sculptur¬ 
ing of the surface. 
In general, although the evidence is still incom¬ 
plete, we seem justified in believing that the pigments 
of butterflies are either modified waste products or 
the dark pigments. From the scales of a large 
number of butterflies Urech did not succeed in a 
single instance in obtaining any pigments which were 
soluble in alcohol, benzol, or the other common 
organic solvents. That is, if we may trust his 
results, lipochromes are absent in the adult. This 
is interesting, not only because of the prominence 
of these pigments in the larvae, but because they are 
so important in coloration in animals nearly related 
to the insects. In Crustaceans, for example, as we 
have seen, the lipochromes colour the shell, the skin, 
and the ova. We have Mr. Poulton’s authority for 
saying that even in Lepidoptera lipochromes still 
colour the ova, though here they are probably 
derived pigments and no longer native, but they 
have in the adult entirely disappeared from the 
cuticle and from the skin so far as external colora¬ 
tion goes, being replaced by modified waste products. 
As a probable exception we may notice the green 
pigment found by Hopkins in the Pieridse ; this must 
surely be one of Mr. Poulton’s derived pigments ! 
