The balbiani body in the female germline cells of an earwig, opisthocosmia silvestris

In the majority of invertebrate and vertebrate species, gametogenesis starts with the formation of cysts (clusters) of sibling germline cells. Cysts originate as the result of mitotic divisions of a specialized germline cell, the cystoblast. Since these divisions are incomplete, the cyst cells (cystocytes) remain connected by stable connections, termed intercellular bridges (ring canals). In forficuloid earwigs, female germ cell cysts are composed of two cells only: the pro-oocte and pro-nurse cells. We show that in Opisthocosmia silvestris, the cystoblast, as well as both cells of the cyst, contain the Balbiani body (Bb), a distinct cytoplasmic organelle composed of numerous mitochondria. We also show that in the cyst cells, the Bbs are invariably located next to the fusome, a specialized cytoplasm occupying the bridge connecting sibling cells.