Electron microscopic analysis of a representative cyst in an ovary from a mature fa/fa rat. a) Photomicrograph of the cyst stained with toluidine blue (Magnification, 100×). b) Electron micrograph of the cyst (magnification, 100×; bar, 2 μm). The region bordering the cyst was comprised of one layer of fibrous cells in addition to theca cells that contained fat deposits. No normal granulosa cells were seen. c) Electron micrograph showing the interior of the cyst (magnification, 2,500×; bar, 2 μm). A possible degenerating oocyte is seen. d) Higher magnification electron micrograph of the homogenous substance showing mitochondria, endoplasmic reticulum and microvilli: S, homogeneous substance; Fc, fiver cell; T, theca cell; *, fat deposit; Mv, microvilli; M, mitochondria; ER, endoplasmic reticulum (magnification, 20,000×; bar, 200 nm).