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 Pierids ; this must 

 surely be one of Mr. Poulton's derived pigments ! 



