154 COLOUR IN NATURE chap. 



green scales of Papilio eurymedes, Urech extracted a 

 yellow pigment which was almost insoluble in water, 

 but which dissolved readily in hydrochloric acid. 

 He adds as a note, however, that the scales retained 

 their green colour after treatment with acid and 

 ammonia. It is almost impossible to doubt that in 

 this case the green colour is structural, the part 

 played by the yellow pigment being uncertain. 

 Further, he found that the green scales of Thecla 

 rubi are yellow by transmitted light, and almost 

 coloiirless when the light falls from the base of the 

 scale upwards, while to hydrochloric acid they yield 

 a yellow pigment. These two cases seem to suggest 

 that in butterflies, as in birds, green may be pro- 

 duced by a combination of a yellow pigment and 

 a structural modification. On the other hand, from 

 the green scales of Sphinx nerei Urech extracted a 

 pigment which was slightly soluble in water and 

 readily soluble in acid and ammonia. Of the three 

 solutions the first was greenish-yellow, the second 

 orange-yellow, and the third green. The addition of 

 ammonia to pigment turned yellow by acid restored 

 the green colour. This fact would suggest that the 

 green pigment of Sphinx nerei is derived from a 

 yellow, in much the same way as is the red pigment 

 of Deilephila. These facts suggest the possibility 

 that a yellow acid body in some way related to 

 lepidotic acid occurs in butterflies outside the Pieridae, 

 capable of acting itself as a pigment and also of 

 giving rise to red (or green ?) pigments. 



Urech (1890) has made numerous observations on 

 the relation between the colour of the urine in butter- 

 flies and the prevalent colours of the scales. His 



