[EN] Ultrastructural studies of oogenesis in Bolinus brandaris are described. Although the initial phase of oogenesis is common to most animal species, vitellogenesis can be considered a species-specific characteristic. In the vitellogenesis of B.brandaris, mitochondria and endoplasmic reticula play a relevant role in the formation of myelinised membranous systems. Nuclear envelope, Golgi body and the oocyte plasma membrane invaginations are three possible origins for annulate lamellae. The latter can be considered membranous reservoirs. There are two sources for the vitellum: exogenous (from follicular cells) and endogenous (from the endoplasmic reticulum of the same oocyte).[ES] Aunque las primeras fases de la oogénesis son comunes a la mayoría de las especies animales, en la vitelogénesis del Bolinus brandaris sin embargo puede considerarse como específica de cada una de ellas, en estre poceso cabe destacar el papel de las mitocondrias y de retículo endoplasmático en la formación de sistemas menbranosos que asemejan figuras mielínicasPeer reviewed