UNFERTILIZED OOCYTES IN STREPTOCEPHALIDS - RESORBED OR RELEASED

Short interval monitoring of isolated females of Streptocephalus dicho tomus Baird, S. proboscideus (Frauenfeld), and S. torvicornis (Waga) r evealed no resorption of unfertilized oocytes in the lateral pouches o f the oviducts or in the ovisac. Oocytes expelled by the female disint egrate in the medium. This finding is in disagreement with earlier stu dies on S. dichotomus and S. proboscideus, but corroborates findings o n S. vitreus (Brauer) and S. rubricaudatus (Klunzinger). Light and ele ctron microscopic studies of unfertilized and fertilized oocytes show polar-body extrusion, vitelline-membrane formation, and egg-shell depo sition in fertilized oocytes only. The streptocephalids studied here d iffer, in this respect, from two other anostracans, Tanymastix and Art emia, where unfertilized oocytes develop a vitelline membrane, and som etimes an egg shell.