An electron microscopic study of vitellogenesis and egg membrane formation in Lytta nuttalli Say (ColeopterarMeloidae)

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Abstract
Vitellogenesis and egg membrane formation in the terminal ovarian follicles of Lytta nuttatii were investigated by electron microscopy. Three kinds of yolk globules are produced. They apparently are composed predominantly of carbohydrates, lipids, and proteins, respectively. The "carbohydrate" and "lipid" yolk are assembled in the ooplasm, the former by rough endoplasmic reticulum and the latter by Golgi complexes. Their production begins early in oogenesis. "Proteid" yolk formation begins somewhat later. The "proteid" yolk globules evidently are formed from exfraovarian materials that pass through large spaces that develop between the follicular epithelial cells, then through the oocyte plasma membrane by pinocytosis. Fairly late in development, glycogen granules appear in the inner ooplasm. In the nearly fully grown follicle, the "membranous system" of the vitelline membrane is elaborated. It probably is formed largely from an electron-dense material of undetermined origin that accumulates outside the bases of the oocyte plasma membrane microvilli. Immediately after completion of the vitelline membrane, the chorion is laid down, presumably from dense globules of material produced by Golgi complexes in the follicle cells.

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