The image in HA3 shows a late primary follicle with stratified columnar follicular epithelium called the membrana granulosa (mg). The outermost layer of the membrana granulosa (arrow) stains more darkly because it has secreted a basement membrane between itself and the surrounding stroma. A thin zona pellucida (arrowhead) can be detected in this late primary follicle, between the oocyte (O) and the membrana granulosa.