Urech has also demonstrated that in many Lepidoptera the color of the urine which is voided upon emergence from the chrysalis is similar to the principal color of the scales. 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 yellow 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 (Pieridæ) 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 Pieridæ, 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 chemically 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 Noctuidæ, Geometridæ, and Sphingidæ likewise consists of a derivative of uric acid, which he calls lepidopteric acid. By prolonged boiling in HCl 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.