Int. J. Insect Morpho,'. & Embryol., Vol, 22. Nos 2-4, pp. 255-269. 1993 0020-7322/93$6.00+.00 Printed in Great Britain (~ 1993PergamonPress Ltd STRUCTURE OF OVARIES AND OOGENESIS IN ENTOGNATHANS (APTERYGOTA) SZCZEPAN M. BILIIqSKI Department of Systematic Zoology, Institute of Zoology, Jagiellonian University, 30-060 Krakdw, Poland Abstract- Two categories of female gonads can be discerned among entognathans. In 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, whereas those of collembolans and campodeids are polytrophic-meroistic. Germ-cell clusters of collembolans and campodeids are always chain-like (non- branched). The oocyte develops from the cell placed centrally within the chain. Other cells become presumptive nurse cells. Differentiated nurse cells synthesize rRNA that is later transferred to the developing oocytes. In the panoistic ovaries (proturans and japygids), oocyte nuclei (germinal vesicles) are large and contain huge, active nucleoli. Three types of reserve materials are deposited in entognathan oocytes: 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 (anagenesis) of entognathan ovaries is discussed. Index ,descriptors (in addition to those in title): Oocyte, nurse cells, germ-cell cluster formation, follicular cells, vitellogenesis, formation of egg envelopes. INTRODUCTION IN MOST modern classifications, entognathous insects are regarded as a sister group of the Insecta (s. str.), and subdivided into 3 orders: Protura, Collembola, and Diplura (Hennig, 1969; Kristensen, 1981). Recently, the analysis and reinterpretation of several morphological characters of recent and extinct diplurans (Testajapygidae; Kukalova- Peck, 1987), have led to the suggestion that this order represents a paraphyletic taxon (Stys and Bilifiski, 1990). Consequently, it has been proposed that Diplura should be split into 2 equally ranked groups: Campodeina and Japygina. This genealogical hypothesis is strongly supported by the distribution of the ovary types among entognathans (see also section on Evolution of entognathan ovaries and Fig. 18). The structure of the female reproductive system, as well as the course of oogenesis, have been analysed, in the representatives of all 4 (or 3) entognathan groups (see Table 1). These studies have clearly shown that along with general similarities between the ovaries of the Entognatha and Insecta (s. str.) some fundamental differences occur. The aim of thJis article is to summarize the present knowledge on entognathan oogenesis with special reference to the germ-cell cluster formation, yolk accumulation, and deposition of egg envelopes. More detailed and comprehensive description of the female reproductive system of entognathans will be presented in the book, The Insect Ovary: 255