[Developmental capacities of abdominal imaginal discs in the blow-flycalliphora erythrocephala. Experimental investigations on the morphology of the abdomen].

The differentiation of abdominal imaginal discs of matureCalliphora erythrocephala larvae has been studied by thermocautery and extirpation of the discs, and by implanting them into larval hosts of the same age. The experiments give information on (a) the morphology of the imaginal abdomen, and (b) the "regulative activitybetween imaginal discs". 1. Within each of the first to seventh larval abdominal segments, we identified two pairs ofabdominal discs, a dorsal and a ventral one (Fig. 6). Besides, the terminal part of the abdomen holds the paired lateral genital discs and the unpaired (median) genital disc, which are of different shape in both sexes (Fig. 9, 10). 2. The imaginal discs of a specific larval segment differentiate only into the integument of the corresponding imaginal segment. The dorsal pair of discs gives rise to the dorsal region (≈tergum, dorsum), the ventral pair to the ventral region of the imaginal segment (≈sternum); the left and the right discs of a larval segment develop into the corresponding halves of the segment in the adult. 3. Thelateral genital discs constitute the imaginal discs of the eighth segment, while thegenital disc includes the imaginal cells of the fused segments 9-11 (Fig. 30). 4. Our experimental results confirm thenumbering of segments in the imaginal abdomen, as proposed by Graham-Smith (1938), Crampton (1942), Hennig (1958), and Salzer (1968). 5. The large tergites of the imaginalpreabdomen consist of an area dorsal to the spiracles, arising from the dorsal abdominal discs, and of parts lying ventral to the spiracles. These ventral parts of the tergite as well as the "pleural membranes" and the sternite originate from the ventral discs (Fig. 31). 6. The small first dorsal plate of themale postabdomen proves to betergite 6. The sclerite, bordering the genital pouch ventrally, belongs to two segments; it should be termedsternite 6+7. The large sclerite, called syntergum 7+8 by Salzer (1968), is formed by several pairs of discs: the left ventral abdominal disc 6, the dorsal and ventral discs 7, and the lateral genital discs (Fig. 31). Thus, we term it thetergosternite 7+8. 7. In the male only the last segments of the postabdomen participate in therotation during metamorphosis: The eighth segment is rotated through 180° (=inversion); the hypopygium (=segments 9-11) is circumverted, i.e. twisted through 360° (Fig. 31). Thus,Calliphora has no "postabdomen circumversum" as Salzer (1968) assumed, but merely a "hypopygium circumversum". 8. Our results (Fig. 32) support the current morphological interpretation of thefemale postabdomen or ovipositor, as proposed by Crampton (1942) and Hennig (1958). 9. Theinternal genitalia of the male (without testes) originate from the genital disc. On the contrary, the female internal genitalia (without ovaries) develop from the lateral genital discs (oviduct, uterus, vagina, spermathecae) and the genital disc (parovaria). A comparison of the developmental capacities of theDrosophila genital disc with those of the lateral and median genital discs ofCalliphora shows that in the female ofDrosophila the equivalents of the lateral genital discs have been incorporated into the genital disc (Fig. 30). 10. Afterelimination of any one of the abdominal or lateral genital discs from the mature larva, the complementary disc of the opposite side gives rise to more than accords to its prospective significance (but see the results of Zalokar, 1943, and Murphy, 1967, on cephalic and thoracic discs inDrosophila). Our data on lateral genital discs do not support the view that the reported increased differentiation is due to a "regulation between discs of a single bicentric field" (Pantelouris and Waddington, 1955). Our data may be explained more easily if we assume the existence of an inhibitory effectin situ between the discs of one pair, which is abolished after elimination of the partner (cf. chapter 6.3.).