Flies from mass cultures of Drosophila melanogaster laboratory-strains of wild, white, and vestigial were collected, starved for 24 hours, and lyophilized while still alive. The dried flies were then homogenized in 0.85 per cent NaCl buffered at pH 7.4, and the resulting suspensions used to immunize rabbits by means of four intraperitoneal injections of increasing dose. No demonstrable differences between the resulting antisera were found in complement-fixation tests against the whole antigens. Optimal-proportion precipitin tests were performed using the clear supernates of the centrifuged antigens. No differences were found in these tests. The tubes from the exact optimal-proportion tests were centrifuged after 24 hours at 6 C, and the supernates used as absorbed sera in precipitin-ring tests against the antigens dissolved in 5 per cent gelatin. If absorption proved incomplete, reabsorptions were performed. By these means the three strains were demonstrated to possess the great bulk of their antigens in common. Wild was demonstrated to possess an antigenic fraction in common with white but not vestigial, a fraction in common with vestigial but not white, and a fraction specific to itself. White was demonstrated to possess antigens in common with each of the other strains, and a fraction specific to itself. Antiserum to vestigial demonstrated that vestigial possesses an antigenic fraction in common with white to the exclusion of wild and a fraction in common with wild alone, but failed to demonstrate a fraction specific to itself. These antigenic differences are not thought to be due only to the single major genic differences between these strains, but rather to multiple genic differences which exist between such unrelated stocks.

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This article is a revised portion of a dissertation submitted to the faculty of the Division of Biological Sciences at the University of Chicago in candidacy for the degree of Doctor of Philosophy.

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