[Spermatogenesis of the Baikal sponge Lubomirskia baicalensis (Pallas). Ultrastructural study].

In the sponge Lubomirskia baicalensis, a representative of the endemic fauna in the Baikal Lake, male specimens were first discovered and successive stages of their spermatogenesis were followed at light and electron microscopic levels. Male sex cells develop in cysts surrounded with a membrane consisting of cells which resemble pinacocytes by their ultrastructure. One sponge, during the period a spermatogenesis, contains in its tissue testicular follicles at various stages of the male sex cells maturation, within every follicle the development occurring more or less synchronously. As a result of transformations taking place in the ultrastructural organization of the spermatid, a primitive type of spermatozoon is forming, without acrosome, with large amount of cytoplasm containing small mitochondria in it.