[Experimental determination of the fate map of the male and the female genital imaginai disc in the blow-flyCalliphora].

1. Both, the male and the female genital discs of matureCalliphora erythrocephala larvae represent broad, dorso-ventrally flattened vesicles, the dorsal and ventral walls of which show characteristically formed papillae and thickenings (Fig. 1). 2. In order to investigate the prospective fate of the various disc regions, specific disc fragments (e.g. dorsal and ventral fragments) were implanted into the body cavity of host larvae of the same age (Fig. 3, 4; Tables 1, 2). 3. The results demonstrate that the genital discs inCalliphora - as those inDrosophila (Hadornet al., 1949; Ursprung, 1957, 1959) - are organized bilaterally symmetrical. They represent a mosaic of individual anlagen or primordia, and, even immediately before puparium formation, are capable of some regulation. 4. In the male and also in the female disc individual anlagen are found in the dorsal as well as in the ventral wall; their arrangement in the disc is illustrated in three-dimensional fate maps (Fig. 5, 6). 5. These fate maps are compared with anlagen plans ofDrosophila andMusca genital discs previously published by other authors.