COLOUR IN NATURE 
CHAP. 
152 
The only other pigment found in the Pieridae is 
the green one described by Mr. Hopkins as occurring 
between the laminae of the wing. This is soluble 
in cold water, contains iron, and gives a spectrum 
with a single well-marked band in the red; it is 
perhaps a blood pigment, and is common among 
the Pieridae. It, however, rarely affects the surface 
coloration, except in the male of Nepheronica lutescens , 
where the blue ground-colour is said to be due to 
this pigment shining through the colourless scales. 
In general, therefore, the pigments of the Pieridae 
are few in number, and the colours are usually due 
to simple pigmental effects. The pigments are uric 
acid, lepidotic acid and that modification of it which 
forms the red pigment, the dull black and brown 
pigments, and the rare green pigment. These pig¬ 
ments rarely occur intermixed, and structural colours 
are typically absent. 
Pigments of other Butterflies 
With regard to the pigments of other butterflies 
there is much less certainty. Hopkins has not 
succeeded in obtaining the murexide reaction outside 
the limits of the Pieridae, and is inclined to think 
that the pigments of the uric-acid group are confined 
to this family. Urech, on the other hand, assumes 
that the pigments of butterflies in general are modi¬ 
fied waste products, which Mr. Hopkins also admits 
as possible. The fact that almost all the bright- 
coloured pigments are soluble in hot water, as well 
as some other reactions, seems to support this view. 
Among butterflies in general the following colours 
