ORIGIN OF THE UNIFLAGELLATE SPERMATOZOON OF BALTOPLANA-MAGNA (PLATYHELMINTHES, KALPYTORHYNCHIA)

An electron microscopic study of sperm and spermiogenesis revealed the process of formation of the monoaxonemal sperm in Baltoplana magna. T wo basal bodies are present in the zone of differentiation of the youn g spermatid, on either side of an intercentriolar body, but only one d evelops into a normal flagellum. The other remains as a flagellar bud that disappears after the spermatid has become elongated and the norma l flagellum has fused with the spermatid shaft in a distal to proximal direction. The mature sperm has a single incorporated axoneme of the trepaxonematan 9+''1'' configuration, a full ring of longitudinal cort ical microtubules, an elongate mitochondrial rod and an elongate nucle us with a number of dense longitudinal chromatin rods. There are no de nse bodies present in the spermatids nor in any region of mature sperm .