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Various observations have been made during recent years, which show that a close association may obtain between pigments which function in ornament and substances of excretory nature. Leydig has shown that, in snakes, certain white and yellowish patches owe their colour to what he considers to be a combination of guanin with a proteid base. In the skin ofChrysochloris he has indicated the probable presence of urates, and has found “guanin-haltiges pigment” in the iris of vertebrates. He has further demonstrated the presence of excretory products in the epidermis ofSyrphus ,Ascellus , and of certain slugs. Eisig has described the association of pigment with excretory substances in the Capitellidæ. Finally, Cunningham and MacMunn have extended the original observation of Barreswil and Voit, who demonstrated the presence of guanin in the scales of fishes, and have fully dealt with the interesting association of this substance with lipochromes and melanins in the same situation. In 1889, I myself showed that the pigment contained in the wings of the yellow Pieridæ was a derivative of uric acid, and suggested that it was related to the substance known as mycomelic acid. A, B. Griffiths has since stated that a green pigment found by him in various species of Lepidoptera is also a uric acid derivative. In the present paper I hope to show more fully that in the Pieridæ the normal excretory products of the insects are, throughout the group, made to subserve the purposes of ornament. The artificial production of the yellow and most important pigment will be discussed, and my original suggestion that it would be found related to mycomelic acid confirmed—to the extent that a proof will be given of its presence in the product described by Hlasiwetz under that name.

XV. The pigments of the Pieridæ: a contribution to the study of excretory substances which function in ornament