CENTRIOLE DEVELOPMENT AND FORMATION OF THE FLAGELLUM DURING SPERMIOGENESIS IN THE OSTRICH (STRUTHIO-CAMELUS)

The formation and development of the ostrich sperm tail follows the ge neral pattern described for vertebrate sperm but differs in a number o f important aspects when compared with other nonpasserine birds. Midpi ece formation is characterised by the development of a long (3 mu m) d istal centriole which determines the length of the midpiece. The dista l centriole surrounds a pair of microtubules embedded in a core of den se material. A prominent annulus, which remains stationary during sper miogenesis, demarcates the midpiece/principal piece junction. Ostrich spermatids display similar cytoplasmic densities (chromatoid body, ann ulus, granulated bodies, reticulated bodies and mitochondria-associate d material) to those observed in mammalian spermatids. In the ostrich, however, the chromatoid body is not observed to contribute towards th e formation of the annulus while the granulated bodies develop within radial bodies and not in their vicinity as in mammals. Whereas in mamm als granulated bodies have been linked to coarse fibre formation they appear to perform a limited function in ostrich spermatids as only rud imentary outer dense fibres are formed. No specific role is attributed to the reticulated bodies but the mitochondria associated material is implicated in the formation of intermitochondrial cement. The formati on of the principal piece and end piece of the flagellum is modelled o n that of the mammalian spermatid. The axoneme emerges from the free e nd of the distal centriole and the ribs and longitudinal columns are p rogressively formed from a layer of amorphous material situated betwee n the axoneme and the plasmalemma. The end piece is formed by an exten sion of the principal piece consisting of axonemal microtubules closel y surrounded by the plasmalemma. The formation of a long distal centri ole containing a central pair of microtubules, the stationary nature o f the annulus and the presence of a ribbed fibrous sheath around the p rincipal pie:ce distinguishes spermiogenesis in the ostrich and rhea f rom that of other nonpasserine birds. These features appear to be char acteristic of more primitive avian families.