[State of determination of imaginal blastemas in embryos of Drosophila melanogaster as revealed by mixing experiments].

Anterior halves, marked with the geneyellow of 10 h old embryos have been intermingeled with posterior halves of the same age, carrying the genesebony andmultiple wing hairs. Series in which only one pair of fragments were combined yielded the same general results as mass-series where forty anterior with forty posterior fragments were mixed. The mixed blastemas are first cultured for two weeks in the abdomen of adult females where they proliferate and terminate the larval differentiation. From these cultures, fragments are implanted back into metamorphosing larval hosts. These implants differentiate by forming normal adult organs. Among them, mosaic structures to which anterior as well as posterior halves contribute, were found only in differentiations belonging to the middle body regions (legs, wings, halteres, abdomen), whereas head structures and genital organs were formed only by cells from anterior and posterior halves, respectively. From these results we conclude that all tested ectodermal cells of embryonic blastemas are differently determined for the specific body regions along the anterior-posterior axis.