The ultrastructure of the spermatozoon and spermiogenesis in Cryptocotyle lingua (digenea: Heterophyidae)

During spermiogenesis two lateral flagellar processes and a median process arising from the apex of the zone of differentiation, fuse to form the elongated unipartite spermatozoon. Two axial units, therefore, with the ‘9+1’ pattern of microtubules are incorporated into the spermatozoon. The nucleus, in the head region, contains dense lamellar subunits arranged in a spiral in the long axis. These are formed by condensation of the chromatin during spermiogenesis. The single elongated mitochondrion, resulting from early fusion of small mitochondria, extends through the head and middle regions of the spermatozoon. Peripheral microtubules, present originally in the zone of differentiation, are arranged in straight dorsal and ventral rows, along the length. β glycogen particles accumulate in the spermatozoa after they have separated from the residual cytoplasm. Spermatozoa are present in the testes on the second day after infection of the bird host and accumulate in the vesicula seminalis from the third day onwards.