Structure of ovaries and oogenesis in Corydalidae and Chauliodidae (Insecta, Megaloptera). I. Architecture of adult ovarioles and previtellogenesis

The results of histological and EM studies on the ovaries of three represen tatives of Megaloptera: Chauliodes pectinicornis, Nigronia fasciata (Chauli odidae), and Corydalus peruvianus Corydalidae) are presented. It is shown t hat the ovaries of all 3 investigated species are panoistic (secondary pano istic, = neopanoistic) and consist of numerous (more than a hundred) ovario les that are differentiated into 3 well-defined regions: the terminal filam ent, the germarium, and the vitellarium. The germaria of adult females are apparently non-functional and contain germ and somatic cells in various sta ges of degeneration. The vitellaria are composed of 12 - 15 developing ovar ian follicles (= oocytes surrounded by follicular cells) in a linear arrang ement. In adult females these follicles can be classified into early previt ellogenic, late previtellogenic, vitellogenic, and choriogenic. During earl y previtellogenesis oocyte nuclei (= germinal vesicles) contain single nucl eolar masses. Histochemical analyses indicate that within the masses DNA as well as AgNOR proteins are present. During subsequent stages of the previt ellogenic growth nucleolar masses gradually break down into smaller aggrega tions of coarse granular material, i.e. multiple nucleoli. In chauliodids t he nucleoli are distributed evenly throughout the nucleoplasm while in the corydalid, C. peruvianus, they form a characteristic ring. The presented re sults are discussed in a phylogenetic context.