[Structural Changes and Histochemical Findings with Special Reference to the Oosome During Oogenesis and Cleavage of Pimpla Turionellae L. (Hymenoptera, Ichneumonidae)]

Oogenesis and cleavage ofPimpla turionellae were studied by conventional histological methods. - The development of the oocytes in the polytroph-meroistic ovariole is subdivided into 10 stages. In stage II, when the nutritive chamber is formed, the young oocyte contains achromidium in the ooplasm, which lies on the membrane of the nucleus, being situated in the center of the cell. In the following stages the chromidium is placed in the lower part of the oocyte. In all stages the nutritive cells are connected with the oocyte by a plasm continuation of the oocyte. The nucleus of the oocyte possesses a caryosphere and severalendobodies ("Binnenkörper") but no nucleoli. In stage V the firstaccessory nuclei appear near the nucleus, which is now situated in the front part of the oocyte. In stage VIvitellogenesis begins along the periphery of the front part of the oocyte. The accessory nuclei are considerably multiplied in the anterior part of the oocyte.Oosome material accumulates around the chromidium, forming a cone-shaped region. In stage VIII the cytoplasm of the nutritive cells streams into the oocyte. The oocyte is filled up with yolk bodies. The oosome material is rounding off. The accessory nuclei dissolve. - The development of the deposited egg was examined until the formation of thepole cells. The oosome reaches the periplasm of the posterior pole, where it spreads. The forming pole cells take up the oosome material.The distribution ofnucleic acids, polysaccharides, proteins andlipids in the cells of the ovariole and egg was analyzed with standard histochemical methods. - In all stages the polyploid nutritive cells deliver RNA substances to the oocyte by means of the plasm continuation. The endobodies of the oocyte nucleus are built up by proteins, RNA is absent. The yolk bodies contain proteins and polysaccharides. The accessory nuclei and the chromidium contain proteins; DNA and RNA could not be demonstrated. In all stages the oosome is rich in RNA. - The egg contains muchfat and glycogen yolk. In the growing oocyte the fat grana appear early. Large amounts of glycogen are deposited in the nearly grown up oocyte.The problems ofgrowth andtectonics of the oocyte and hypotheses of the oosome function during the proliferative growth of the oocyte and later on during embryonic development as a factor predisposing the fate of pole cells are discussed.