[Effect of nitrogen mustard on the development of the bristle organ and on the rate of transdetermination ofDrosophila melanogaster].

1. Injection of nitrogen mustard (HN-3) into late third instar larvae ofDrosophila melanogaster and treatment of male foreleg disks with HN-3in vitro results in the following: formation of fewer bristles and hairs, reduction in size of leg parts, alteration of normal bristle patterns, and differentiation of bristle organs without sockets and bracts. 2. When disks, treated with HN-3, were cultivated in adult hosts for 14 days before transplantation into metamorphosing larvae, mostly complete bristle organs were formed, whereby bristles of distal leg parts usually form bracts. 3. Transdetermination is completely suppressed after HN-3-treatment, although proliferation occurs in disks treated with a concentration of 0,02 Μl HN-3 per ml Insect-Ringer. 4. Injection of HN-3 into late third instar larvae results in the induction of somatic mutations. 5. The effect of nitrogen mustard is compared with the effect of mitomycin C treatment and discussed with respect of the suppression of transdetermination.