Oogenesis in the silkworm, Bombyx mori, was studied by light and electron microscopy of sections of resin-embedded follicles. The development of the follicles was divided into a series of 12 distinctive stages based on various morphological criteria. Structural changes in the oocyte, nurse cells, and follicle cells are described and illustrated.

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The formation of the micropylar apparatus during oogenesis in the silkworm, Bombyx mori, has been studied using light and transmission electron microscopy. The micropylar apparatus is formed by three types of cells: the micropylar channel-forming cells (MCFCs), the micropylar orifice-forming cells (MOFCs), and the micropylar rosette-forming cells (MRFCs). During the formation of the vitelline membrane and the chorion, each of the MCFCs extends a cytoplasmic projection serving as the mold of a micropylar-channel into the egg envelopes. The detachment and collapse of the projections takes place at the end of choriogenesis. The micropylar channels possess a common external orifice on the chorion and several internal orifices within the vitelline membrane. The MOFCs interact closely with the MCFCs and contribute to the formation of the external micropylar orifice. A petal-like rosette surrounding the orifice is imprinted on the outer chorionic surface by the MRFCs which enclose a group of the MCFCs and MOFCs.