Structural aspects of ovarian sheaths inPhormia regina(Meigen) (Diptera, Calliphoridae)

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Abstract
Each ovary in Phormia regina consists of numerous meroistic ovarioles held together by an ovarian muscle sheath. Each ovariole is enclosed by a thin ovariolar sheath that becomes continuous with the more external ovarian muscle sheath at the germarial tip. In previtellogenic and early vitellogenic ovaries, terminal follicles are connected to the lateral oviducts through a system of ovarian tubules and ducts. Ovarian tubules establish a continuity between the ovariolar sheath of terminal follicles and the ovarian ducts. The latter form a system of branching luminal continuities that run underneath the ovarian muscle sheath. While ovarian ducts are permanent structures in the ovary, ovarian tubules are restricted to early vitellogenic ovaries. In ovaries at more advanced stages, terminal follicles connect directly to the ovarian ducts over the convex side of the ovary. Thus, on this convex side the ovary is surrounded by a sheath‐like covering. We suggest that the various sheaths are so disposed as to allow a directional flow of hemo‐lymph through the ovary to gain access to each terminal follicle.