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.