Scanning electron microscopy of the Graafian follicle during ovulation in the golden hamster.

Ovaries from hCG-injected hamsters were examined during a timed series starting 14 h before and ending 4 h after expected ovulation. Beginning about 4 h before expected ovulation, large wrinkles were seen at the bases of follicles as stigma formation began. Apical surface epithelial cells were frequently found in folds bordering small areas where widely separated surface cells 'floated' on a slightly bulging underlying basal lamina. The small stigma receded, and an upright column of underlying cells formed followed by the ejection of the oocyte mass. The post-ovulatory rupture site was a cavernous opening in which red blood cells, tunica albuginea cells, and fibroblast-like cells were observed.