152 COLOUR IN NATURE chap. 



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 



