STRUCTURE OF OVARIES AND OOGENESIS IN ENTOGNATHANS (APTERYGOTA)

Two categories of female gonads can be discerned among entognathans. I n Protura, Collembola and Campodeina (Apterygota), the paired ovaries are sac-shaped, not divided into discrete ovarioles. In contrast, the ovaries of Japygina are composed of 7 metamerically arranged ovarioles . The ovaries (ovarioles) of proturans and japygids are panoistic, whe reas those of collembolans and campodeids are polytrophic-meroistic. G erm-cell clusters of collembolans and campodeids are always chain-like (non-branched). The oocyte develops from the cell placed centrally wi thin the chain. Other cells become presumptive nurse cells. Differenti ated nurse cells synthesize rRNA that is later transferred to the deve loping oocytes. In the panoistic ovaries (proturans and japygids), ooc yte nuclei (germinal vesicles) are large and contain huge, active nucl eoli. Three types of reserve materials are deposited in entognathan oo cytes: lipid droplets, yolk spheres, and characteristic dense granules . Vitellogenesis is of a mixed type. Egg envelopes are secreted by the follicular cells and/or by the oocyte. The possible evolution (anagen esis) of entognathan ovaries is discussed.