The pattern of fluorescent substances in Drosophila testes was qualitatively and quantitatively investigated through paper chromatography and fluorescence measurements. The pteridine inventary which is similar to that found in eyes, is quantitatively altered by a number of mutants of Drosophila melanogaster. Different species of Drosophila are characterized by specific patterns. The red pigments found in the testes of some species of Drosophila are chromatographically identical with the

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... al with the drosopterines of the eyes.