The ovaries of the common wasp, Vespula germanica are polytrophic-meroistic and consist of 2-3 (workers) or 7 (queens) ovarioles. The ovarioles are differentiated into three regions: a terminal filament, a germarium, and a vitellarium. The germaria of both castes consist of two zones: an anterior zone of germ-cell cluster formation and a posterior one of germ-cell cluster differentiation. The vitellaria comprise 4 ? 6 (workers) or 7 ? 10 (queens) ovarian follicles (egg chambers). Each chamber consists of an oocyte and about 60 isodiametric nurse cells (trophocytes). The egg chambers have been arbitrarily classified into four developmental categories: early and late previtellogenic, vitellogenic, and choriogenic. The process of oogenesis in workers proceeds only up to the onset of the late previtellogenesis. Neither vitellogenic nor choriogenic egg chambers were observed in this caste. During early and late previtellogenesis the envelope of the oocyte nucleus proliferates and becomes highly folded. This process leads to the formation of characteristic organelles, termed accessory nuclei (AN). Although AN arise in the oocytes of both queens and workers, their number in the latter caste is always considerably lower. At the onset of the late previtellogenesis AN start to migrate towards the periphery of the oocyte where they reside till the end of oogenesis. The physiological state of the worker ovaries is discussed in the light of the presented results.
The structure of the ovaries in three representatives of Hydradephaga (Haliplus flavicollis, Gyrinus natator and Orectochilus villosus) and one of Geadephaga (Carabus variolosus) was studied. In all the investigated species the ovarioles are of the meroistic polytrophic type. Within ovarioles several egg chambers occur, clearly separated into two compartments: one occupied by nurse cells and the other by an oocyte. The analysis of serial semithin sections revealed that the clusters of the germ cells are branched and that there are always 7 nurse cells in the egg chambers in the examined Hydradephaga. In contrast, the number of nurse cells in Carabus variolosus egg chambers is variable and much greater (around 60). In addition, in the last species a few trophocytes were found containing 2 nuclei. In view of the results obtained the possible phylogenetic implications are discussed. A tentative hypothesis is proposed that a small and constant number of the nurse cells might be a plesiomorphic condition for the suborder Adephaga.
In insect ovaries, germ line cells are surrounded by somatic cells that initially form a uniform follicular epithelium. The subsequent diversification of the follicular cells into several subpopulations enables specification of distinct structures in different regions of complex eggshells. It also influences the patterning of the future embryo. These processes have been extensively studied at both the cellular and molecular levels using the Drosophila ovary as a model system. It is not clear however, to what extent the Drosophila model of the follicular epithelium patterning is universal for the entire Diptera group. Here, we analyze the diversification of the follicular cells in a distant Drosophila relative, the horse fly, Haematopota italica. We found that in this species, there are 6 recognizably different follicular cell subpopulations within the previtellogenic ovarian follicles. Ultrastructural analysis of the follicular epithelium revealed two morphologically distinct clusters of follicular cells residing at the anterior and posterior poles of the follicles. Each cluster consists of 2-3 polar cells located centrally and surrounded by several outer cells called border cells (at the anterior pole) or border-like cells (at the posterior pole). During previtellogenesis, the clusters lose the initial symmetry as their cells differentiate and develop conspicuous cytoplasmic projections comprising cytoskeletal elements. Ultimately, the follicular cells of the anterior and posterior clusters become morphologically different and, as we suggest, participate in different processes during oogenesis and formation of the and, eggshell in H. italica.
The results of histological and EM studies on the ovaries of three representatives of Megaloptera: Chauliodes pectinicornis, Nigronia fasciata (Chauliodidae), and Corydalus peruvianus Corydalidae) are presented. It is shown that the ovaries of all 3 investigated species are panoistic (secondary panoistic, = neopanoistic) and consist of numerous (more than a hundred) ovarioles that are differentiated into 3 well-defined regions: the terminal filament, the germarium, and the vitellarium. The germaria of adult females are apparently non-functional and contain germ and somatic cells in various stages of degeneration. The vitellaria are composed of 12 ? 15 developing ovarian follicles (= oocytes surrounded by follicular cells) in a linear arrangement. In adult females these follicles can be classified into early previtellogenic, late previtellogenic, vitellogenic, and choriogenic. During early previtellogenesis oocyte nuclei (= germinal vesicles) contain single nucleolar masses. Histochemical analyses indicate that within the masses DNA as well as AgNOR proteins are present. During subsequent stages of the previtellogenic growth nucleolar masses gradually break down into smaller aggregations of coarse granular material, i.e. multiple nucleoli. In chauliodids the nucleoli are distributed evenly throughout the nucleoplasm while in the corydalid, C. peruvianus, they form a characteristic ring. The presented results are discussed in a phylogenetic context.
Each of the 2 ovaries of Neotituria kongosana consists of 7 telotrophic ovarioles. Within the ovariole, the terminal filament, germarium, vitellarium, and pedicel can be distinguished. The terminal filaments are composed of disc-shaped basal cells and elongated apical cells, oriented parallel to the long ovariole axis. The apical and lateral aspects of the tropharium are encompassed by a single layer of somatic cells termed inner sheath cells. These cells are diversified into larger apical inner sheath cells (AISC) and much smaller lateral inner sheath cells (LISC). The tropharium is filled with numerous individual trophocytes (= nurse cells). All the trophocytes are surrounded by complete plasma membranes and are joined to a centrally located trophic core by means of narrow cytoplasmic extensions, termed trophic processes. The terminal filament is separated from the rest of the ovariole by a relatively solid transverse septum. It is suggested that the material constituting the septum is synthesized by 2 types of cell, namely the AISC and the basal cells of the terminal filament. Anagenesis of hemipteran ovarioles is discussed in relation to the findings presented.
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