Muco‐follicle cells of the jelly coat in the oocyte envelope of the sheatfish (Silurus glanis L.)

During early vitellogenesis of the oocytes of Silurus glanis, the follicular cells proliferate, their epithelial organization becomes disrupted, and they transform into an irregularly structured large mass of cells engaged in intensive secretory activity. They contain nuclei, rough endoplasmic reticulum, Golgi bodies, and secretory inclusions termed “acorn bodies,” which are synthesized in the cytoplasm. The acorn bodies have two components: an electron‐dense cap and a moderately electron‐dense body. As development proceeds, the acorn bodies become modified into spherules of mucous material, the mucosomes. The electron‐dense part persists as a small calotte or crescent often irregularly structured at the periphery of the mucosome, and fragments of it are dispersed into the interior of the mucosomal body. The mucosomes are membrane‐bound and contain small granules, 55 nm in diameter.