Figure 6 in Position and development of oocytes in velvet worms shed light on the evolution of the ovary in Onychophora and Arthropoda

Figure 6. Internal organization of the pseudoendogenous ovary in Metaperipatus inae (A–E) and Metaperipatus blainvillei (F). Light micrographs (A, B) and transmission electron micrographs (C–F). A, cross-section of the ovary (dorsal is up). Note the lateral position of the crescent-shaped ovarian lumen (lu) and the central position of the germinal epithelium (ge). B, detail of stalked oocytes (oc) from the germinal epithelium, which do not bulge into the haemocoel but retain their position within the ovary. C, detail of cells (ce) surrounding a maturating oocytes in the germinal epithelium. D, detail of a stalk. Arrows indicate the intermediate filaments. E, detail of the lumen and ovarian epithelia. The epithelial cells are connected by an apical junction (arrowhead). F, lateral ovarian wall consisting of the sterile epithelium (se) and connective tissue containing muscle cells (mc), a haemocyte (he), and sperm (sh). Abbreviations: bl, basal lamina; ce, cells associated with an oocyte; cg, collagen fibres; ct, connective tissue; ge, germinal epithelium; hc, haemocoel; he, haemocyte; lu, ovarian lumen; mc, muscle cell; mv, microvilli; nl, nucleolus; nu, nucleus; oc, maturating oocyte; se, sterile epithelium; sh, sperm head; st, stalk; sw, sterile ovarian wall.