Fig. 1. Development of the genital disc and adult derivatives in both sexes. The female and male genital discs are shown as ventral, dorsal and parasagittal views. A8 (female primordium, pink), A9 (male primordium, blue) and A10-11 (anal primordium, green) indicate the corresponding abdominal segments. The posterior compartment of each primordium is shown in darker colours (pink, blue and green). Note that each posterior compartment is adjacent to the anterior cells corresponding to its own segment and to the anterior cells of the following segment, as occurs in the abdomen (parasagittal view). The P compartment cells of the three segmental primordia converge in the lateral areas (asterisk) but not in the centre of the disc. A, anterior compartment; P, posterior compartment; FGP, female genital primordium; MGP, male genital primordium; AP, anal primordium; RFP, repressed female genital primordium; RMP, repressed male genital primordium. External female terminalia: dAp, dorsal anal plate; vAp, ventral anal plate; T8, tergite eight; dVu, dorsal vulva; vVu, ventral vulva; dVp, dorsal vaginal plate; vVp, ventral vaginal plate. Internal female terminalia: U, uterus; Sr, seminal receptacle; Spt, spermatheca; Pov, parovaria; Od, oviduct (connected to the ovaries). Male external terminalia: Ap, anal plate; Ga, genital arch; Ll, lateral lobe; Lp, lateral plate; Cl, clasper; PA, penis apparatus. Internal male terminalia: Ed, ejaculatory duct; Sp, sperm pump; Pg, paragonia (male accessory gland); Vdef, vas deferens (connected to the testes). Modified, with permission, from Epper and Nöthiger (Epper and Nöthiger, 1982) and P. C. Ehrensperger (PhD thesis, University of Zürich, Switzerland, 1983).

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