ELECTRON-MICROSCOPE OBSERVATIONS ON OVARIAN FOLLICLE OF DOMESTIC-FOWL DURING RAPID GROWTH PHASE

Abstract

Rapid growth of the ovarian follicle of the fowl (Gallus domesticus) results from the deposition of yellow yolk in the oocyte. In the follicle the oocyte is enclosed in a thin, but complex sheath of vascularized tissue. The theca externa, composed of layers of collagen fibers and flattened, fibroblast-like cells with abundant cortical microfilaments, provided mechanical support for the expanding oocyte. The narrower theca interna contained a capillary network, groups of interstitial cells associated with nerve fibers, and a discontinuous layer of fibroblasts adjacent to a basal lamina, 1.0 .mu.m thick, which surrounded the granulosa. The granulosa cells possessed prominent Golgi elements, diverse granules and vesicles, macrovilli and microvilli. The macrovilli, protruding through the perivitelline layers into deep pouches in the oocyte surface, served to anchor the granulosa to the oocyte by means of attachment devices at their tips. The following features were related to the transport of macromolecular components from the vasculature to the oocyte: fenestrations in the endothelium of the thecal capillaries, free erythrocytes in the theca interna, abundant 20-30 nm particles in the basal lamina, wide spaces between the granulosa cells and the open meshwork of the fibrous perivitelline layer. Numerous coated pits and vesicles, 0.25-0.35 .mu.m diameter, in the highly convoluted surface layer of the oocyte provided a mechanism for the incorporation of yolk precursors by pinocytosis.