Fig. 5. Photomicrographs of sections of ovarian pieces stained with haematoxylin and eosin. (A) Uncultured ovary at P0 containing oogonia (open arrowhead) and primordial follicles (closed arrowhead). (B) P0 ovary cultured for 7 days, which contains many growing, primary follicles with larger oocytes (arrowhead). (C) P0 ovary cultured for 7 days in the presence of 100 nM K252a (which inhibits oocyte survival). The ovary contains some oocytes and large areas of cell death. (D) P0 ovary cultured for 7 days in the presence of 40 ng ml^–1 bFGF contains many healthy follicles. (E) P0 ovary cultured for 7 days in the presence of 100 nM K252a and 40 ng ml^–1 bFGF. The ovary has been rescued from the effect of K252a and contains many healthy follicles. (F) Uncultured ovary from E16.5 mouse containing oogonia (arrowhead) but no follicles. (G) E16.5 ovary cultured in control medium for 4 days contains many follicles, all of which are at the primary, growing stage with rounded granulosa cells (arrowhead). (H) Ovary at P0, an equivalent age for the cultured ovary shown in G, with follicles at the primordial, resting stage with flattened granulosa cells (arrowhead). Scale bars: 20 µm.