Spermiogenesis in the pseudophyllid cestode Eubothrium crassum (Bloch, 1779)

Spermiogenesis of the pseudophyllidean tapeworm Eubothrium crassum has been described by the aid of transmission electron microscopy for the first tim e. Initially, early spermatids form a distal cytoplasmic protrusion, a diff erentiation zone containing a small electron-dense, apically oriented regio n. Out of this region, two centrioles with rootlets develop. The centrioles become orientated in the same plane with the appearance of an intercentrio lar body. Now, the long axes of the rootlets are parallel with each other a nd with the long axis of the nucleus. Two flagella of subsequently unequal length are formed very rapidly. Simultaneously, a median cytoplasmic proces s (MCP) develops distal to the flagella. Two arching membranes appear at th e base of the differentiation zone. Each flagellum, still being in contact with an intercentriolar body, rotates to a position parallel with the MCP. The nucleus migrates very rapidly into the MCP at this stage. Subsequently, the two flagella fuse with the MCP. Finally, the basal bodies with the roo tlets detach from the flagella, the intercentriolar body changes its struct ure and spermatids are pinched off from a condensing residual cytoplasm at the level of the arching membranes.