The ovarian area of the gonad. Ovarian area of the gonad at different stages of the second RC stained with hematoxylin-eosin (a-e,g-i) and immunostained with BrdU mAb (f, inset f). The ovarian epithelium forms longitudinal lamellae that extend into the central ovarian cavity (a). A squamous epithelium lines these lamellae at the luminal surface, below which a group of undifferentiated somatic cells were observed (b). The ovarian lamellae are formed by nests of oogonia (c), pre-perinucleolar oocytes (d), early and late perinucleolar oocytes (e), yolk vesicle oocytes (e) and secondary (g) and tertiary (h) yolk vesicle oocytes. Oogonia (f) and somatic cells (inset f) only proliferated during testicular involution. Some atretic follicles were observed in the ovarian of males at the beginning of the third RC (i). Scale bar = 100 μm (a,h), 50 μm (g), 25 μm (e,f,i, inset f) and 10 μm (b-d). OL, ovarian lamellae; OC, ovarian cavity; EPO, early perinucleolar oocytes; LPO, late perinucleolar oocytes; YVO, yolk vesicles oocytes; (arrow heads), proliferative cells; (asterisk), ovarian somatic cells; (white arrows), epithelium lines the ovarian lamellae; (white arrows heads), follicular epithelial cell layer.