ULTRASTRUCTURE OF THE MALE REPRODUCTIVE-ORGANS IN THE INTERSTITIAL ANNELID SPHAEROSYLLIS-HERMAPHRODITA (POLYCHAETA, SYLLIDAE)

The reproductive organs of the simultaneous hermaphrodite Sphaerosylli s hermaphrodita (Syllidae, Exogoninae) were examined by TEM and recons tructed from ultrathin serial sections, Oocytes are produced in the 11 -13th chaetigerous segments and then attached to the outer body surfac e. The male organs comprise a seminal vesicle, testes, sperm ducts and copulatory chaetae. The unpaired seminal vesicle is an uncompartmente d cavity above the gut and within the chaetigerous segments 8-10. Its interior is lined with a layer of gland cells that degenerate as sperm atogenesis in the vesicle proceeds. The testes are situated ventrolate rally, close to the seminal vesicle in the 9th chaetigerous segment. T hey contain cells at early stages of spermatogenesis, which are connec ted to one another by zonulae collares. The testes and seminal vesicle are enclosed in epithelia. Paired sperm ducts run ventrally from abou t the midline of the body under the seminal vesicle and into the para- podia of the 9th chaetigerous segment. There they open, together with the protonephridia of this segment, to the outside next to the stout c opulatory chaeta. Each sperm duct consists of six cells, the luminal s urface of which bears microvilli but no cilia. Only in animals with fu lly differentiated sperm does the small opening of the proximal duct c ell in each duct give access to the seminal vesicle. The mode of sperm transfer is discussed.