Morphological Modifications of Oocyte Vitelline Envelope from Bufo arenarum during Different Functional States. (vitelline envelope/amphibian eggs/fertilization)

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Abstract
The submicroscopic morphology of the vitelline envelope of B. arenarum''s oocyte changes significantly during the maturation and fertilization processes. The morphological changes are related to physiological activity in vivo and can be triggered in vitro by experimental procedures. Ultrastructural differences of fascicular components of the vitelline envelope are presented in coelomic, pars recta conditioned, oviductal, oviposited and fertilized oocytes. Artificial pars recta treatment of coelomic oocytes arrange the fascicular components as those of oviposited oocyte, although differences still remain, indicating that additional maturation processes take place while the egg passes through the oviduct. Fertilized or activated oocytes which are refractary to sperm penetration change the vitelline envelope fascicular components'' orientation, giving a submicroscopical image quite different to those of nonfertilized oocytes. These ultrastructural changes define in a clear-cut manner the functional states of B. arenarum''s oocyte.