MORPHOGENESIS OF THE GENITAL DUCTS AND SPERMATHECAE CLITELLIO-ARENARIUS, HETEROCHAETA-COSTATA, TUBIFICOIDES-BENEDII (TUBIFICIDAE) AND STYLARIA-LACUSTRIS (NAIDIDAE) (ANNELIDA, OLIGOCHAETA)

The development of the male genital ducts in Clitellio arenarius, Tubi ficoides benedii, Heterochaeta costata (Tubificidae) and Stylaria lacu stris (Naididae) is studied with the purpose of investigating the homo logies between different parts of the ducts. In both Tubificidae and N aididae, the male duct comprises a funnel, a vas deferens and an atriu m. There may also be a prostate gland (diffuse or compact) in associat ion with the duct. The funnel and vas deferens, in all four species, o riginate from the peritoneal (mesodermal) cells in the posterior septa in the testes segment, whereas the atrium develops from an epidermal (ectodermal) invagination. The prostate glands have different origins in different taxa; in S. lacustris it differentiates from the peritone al (mesodermal) cells surrounding the atrium, but in H. costata and T. benedii it develops by a multiplication of the atrial (ectodermal) ce lls; C. arenarius lacks a prostate gland. The development of the sperm athecae and the female duct is also studied. The spermatheca is an epi dermal invagination. The female duct is of mesodermal origin. However, the position of the duct differs; in S. lacustris the female duct is lateral and the pore is in the ovarian segment, while in the tubificid s studied the duct is ventral with the pore in the segment behind the one containing the ovary. (C) 1997 The Royal Swedish Academy of Scienc es.