Differentiation of ovariolar follicular cells and formation of previtelline-membrane substance in Simulium Vittatum Zetterstedt (Diptera : Simuliidae)

Abstract

In the cytoplasm of ovariolar follicular cells of newly emerged black flies, free ribosomes were predominant and few strands of endoplasmic reticulum were observed. Golgi complexes were well developed, but no electron-dense secretions were seen within the Golgi vesicles. At the end of day 2, while vitellogenesis was most active and endoplasmic reticulum prevailed in the cytoplasm of the follicle cells, Golgi vesicles containing dense material were observed. Dense droplets were abundant in the cytoplasm adjacent to the microvilli, as well as among the microvilli. At the end of day 3, during which vitellogenesis was complete, the Golgi complexes, containing both dense and fibrous materials, became very prominent in the follicular-cell cytoplasm. The cisternae of the endoplasmic reticulum became dilated and some long strands of endoplasmic reticulum were organized into concentric whorls. At this stage the deposited, previtelline-membrane substance between the follicular cells and the oocyte began to coalesce and gradually formed the vitelline membrane.