Reproductive anatomy and gametogenesis in Shipleya inermis (Cestoda: Dioecocestidae).

Study of the reproductive anatomy in 65 strobilae of the dioecious cestode Shipleya inermis Fuhrmann, 1908 (Acoleata: Dioecocestidae) showed that a common genital duct, probably arising through fusion of the vas deferens and the proximal portion of the vaginal duct, compensated functionally for the loss of a patent vagina. Gonochorism was characteristic, but rudimentary genital organs of the opposite sex were present in 26% of males and 9% of females; two strobilae (3%) were hermaphroditic. Hermaphrodites had normally developed male organs and were capable of cross-fertilization as males; their female organs were much reduced in size but were functional, and eggs or fertilized ova in the uteri indicated that self-fertilization occurred. Gametogenesis was traced, mainly in chromosomal preparations. The diploid chromosomal complement in embryos and germ-line cells consisted of four pairs of homologues (2n = 8, n = 4, FN = 14). Based on observation in female cestodes of one pair of chromosomes having non-homologous or non-pairing segments due to influence of heterochromatin, the authors suggest that females produce gametes of two types relative to heterochromatic DNA, while males are homogametic, and that sex-determining effects are associated therein. In males, meiosis included chromosomal pairing and recombination, after which heterochromatin was eliminated from germline cells through fragmentation. Other biological characteristics of S. inermis in the hosts, Limodromus spp. (Charadriiformes), are briefly discussed.