CHEMICAL NATURE OF THE PK1MKNT 207 



Hopkins has worked on the pigments within the scales of butterflies. The 

 yellow pigment in Gonopteryx rhamni is a derivation of uric acid, and he calls 

 it lepidotic acid. Its aqueous solution is strongly acid to litmus, and must be 

 bad-tasting to birds. 



Hopkins has dissolved the red pigment from the border of the hind wing of 

 Delias eucharis, an Indian butterfly, in pure water, finding as the result a yel- 

 low solution ; but if the solution be evaporated to dryness, the solid residue of 

 pigment is red once more. He has obtained from this pigment of eucharis a 

 silver compound which contains a percentage of metals exactly equal to that 

 from the pigment of G-. rhamni. (Nature, April 2, 1892.) 



"The scales of the wings of the white butterflies (Pieridse) are also shown 

 by Hopkins to contain uric acid, this substance practically acting as a white 

 pigment in these insects. A yellow pigment, widely distributed in the same 

 family, is shown to be a derivative of uric acid, and its artificial production 

 as a by-product of the hydrolysis of uric acid is demonstrated. That this yellow 

 pigment is an ordinary excretory product of the butterfly is indicated by the 

 fact that an identical substance is voided from the rectum on emergence from 

 the pupa. These excretory pigments, which have well-marked reactions, are 

 apparently confined to the Pieridse, and are not found in other Rhopalocera. 

 This fact shows that when a Pierid mimics an insect belonging to another group, 

 the pigments of the mimicked and mimicking insects, respectively, are chemi- 

 cally quite distinct. Other pigments existing, not in the scales, but between the 

 wing-membranes, are shown to be of use for ornament." (Proc. Royal Soc., 

 London, 1894.) 



Griffiths (1892) claims that the green pigment found in several species of 

 Papilio, Hesperia, and Limenitis, also in Noctuidse, Geometridse, and Sphingidse 

 likewise consists of a derivative of uric acid, which he calls lepidopteric acid. 

 By prolonged boiling in HC1 it is converted into uric acid. 



Spuler, however, finds that green does not depend on pigmentation, but is an 

 optical color. As remarked by Spuler, either the chitin of the scales itself is 

 colored reddish (yellow grayish), or the pigment is secreted in the nuclei. 



A. G. Mayer believes that the pigments of the scales are derived 

 from the haemolymph or blood of the pupa, for the following 

 reasons : (1) He is unable to find anything but blood within 

 the scales during the time when the pigment is formed. (2) In 

 Lepidoptera generally the first color to appear upon the pupal 

 wings is a dull ochre-yellow, or drab, and this is also the color 

 assumed by the blood when it is removed from the pupa and ex- 

 posed to the air. (3) He has succeeded by artificial means in manu- 

 facturing several pigments from the blood which are similar in 

 color to various markings upon the wing of the imago ; chemical 

 reagents have the same effect upon these manufactured pigments 

 that they do upon the similarly colored pigments of the wings. " It 

 should be here noted," he says, "that in 1866 Landois pointed out 

 the fact that the color of the dried blood of many caterpillars is 

 similar to the ground color of the wings of the mature insect." 



Ontogenetic and phylogenetic development of colors. The colors of 

 the wings of Lepidoptera, as is well known, are acquired at the end 



