Abstract
Mutants of Drosophila melanogaster capable of ommochrome formation store oxykynurenin in the Malpighian tubes during the larval stage. The product occurs in the form of yellow, osmiophile concrements in bubble-like widenings of the endoplasmatic canal system of Malpighian tube cells. The deposits disappear during the pupal rest but reappear again in the imagos, although in smaller amounts. The oxykynurenin which can be identified certainly by chemical and spectrometric methods is lacking in the Malpighian tubes of the red and white-eyed mutants.