The Balbiani body in the oocytes of a common cellar spider, Pholcus phalangioides (Araneae: Pholcidae).

Previtellogenic oocytes of a common cellar spider, Pholcus phalangioides, contain a single aggregation of organelles referred here to as the Balbiani body. It is a well defined ooplasmic structure predominantly composed of fine granular nuage, RNA rich material but comprising also mitochondria, vesicles of endoplasmic reticulum and stacks of Golgi cysternae. The Balbiani body originates early during previtellogenesis in the form of a cap-shaped mass in juxtaposition to one pole of the oocyte nucleus. During later stages of previtellogenic growth the Balbiani body translocates as a single body towards the ooplasm periphery. The results presented indicate that Balbiani body translocation is cytoskeleton independent. Balbiani body repositioning does not result in the localization of its components to any distinct, asymmetrically situated region of the ooplasm but, instead, ends up with their even dispersion in the oocyte cortex. The Balbiani body in Pholcus does not seem to be implicated either in germ cell determination or organelle inheritance. Its homology with similar organelle accumulations in the oocytes of other species is discussed.