1. Genital-imaginal discs of femaleDrosophila melanogaster were fragmented or locally damaged and then culturedin vivo in the abdomens of adult flies (technqiue:HADORN, 1963). The proliferation rate of the autotypic anlagen, as well as the frequency and the quality of allotypic differentiation after transplantation in larvae undergoing metamorphosis, were studied. 2. Only the anlagen of the anal plates can he extensively cultured. Blastemas of soft parts and of vaginal plates have a low proliferation capacity. 3. The rate of transdetermination is very high for the anlage of the anal plates. The blastemas of other autotypic elements rarely transdetermine and they only form small allotypic areas. 4. Transdeterminations originating from anlagen of anal plates are correlated with an enlargement of the autotypic blastemas. In contrast, the occurence of transdetermination in anlagen of the vaginal plates is correlated with a multiplication of the entire genitalia. 5. Twenty-four different allotypic structures which are normally derived from the antennae-, leg-, wing- or clypeo-labrum primordia have been observed. 6. After a first transdetermination step (initial cases) the anlagen of the anal plates form new anlagen, namely of the praefrons, the basis of the maxillary palpus (Rostralhaut), femur and tarsus. From these "primary formation centers" successive steps are possible as in normogenesis. The anlagen of the allotypic third antenna segment behaves as a "secondary formation center", which will differentiate leg, wing and possibly palpus after it has passed further secondary transdetermination steps. 7. According to the observed frequencies, the segments of the allotypic antennae are formed one after another. 8. The organisation and the typical pattern of the allotypic organs are identical to those formed in normal development. 9. The daughter cells of a single cell of a determined blastema are able to produce normal anlagen which are competent to form an integrated pattern. Such a cell can form qualitatively different allotypic blastemas which each correspond to a different imaginai disc.

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Imaginal discs ofDrosophila melanogaster larvae, 24-53 hrs after oviposition, were transplanted into mature immobile larval hosts. The transplants did not respond to the hormonal stimuli of metamorphosis, but instead completed their larval development. When reinjected into mature larval hosts, they now differentiated the full set of their presumptive imaginal structures. The process of acquiring competence for metamorphosis appears to be independent of the hormonal conditions.

These observations lead to the assumption that 2 different mechanisms are responsible for the atheromatosis.