On the cloacal region of Anura in particular of larval Ascaphus

[摘要] ENGLISH ABSTRACT: The ontogeny of the cloacal region of Ascaphus is described from limitedlarval material (beginning approximately at the stage of hind-limb buddevelopment). A comprehensive series of Bufo angusticeps larvae and latepre-larval embryos were used for comparison. The adult and/ or late larvalconditions of the cloacal region in Ascaphus, Bufo, Bombina, Leiopelma, Ranaand Xenopus arc compared.The rods of Noble supporting the cloaca in Ascaphus and the tendinoussheet connecting these with the epipubis are shown to be modifications of aninterfemoral ligament present, with thickened lateral margins, in all theAnura studied. The cloacal lips differentiate early in metamorphosis inAscaphus and Bufo and bear similar relations to the interfemoral ligamentin these and other Anura, so that they are apparently homologous. The posteriorpart of the urodaeum is lengthened in the adult male Ascaphus to form thetail (phallus).The hind-limb anlagen of Ascaphus appear directly beneath the spinalmyomeres and immediately behind the posterior tips of the abdominal musclecords. In Ascaphus, Bufo and Bombina the abdominal muscles (metamericallydisposed in Ascaphus and Bufo) are initially attached posteriorly to the spinalmyomeres but are separated from them anteriorly. lt is probable that themm. compressores cloacae are derived from the hind-limb anlagen. In allAnura examined, including members of all the South African families, thea. ischiadica and n. ischiadicus have a small muscle (designated m. circumflexorarteriae) associated with them; it is presumably capable of compressingthe artery against the nerve.The cloacal region of Ascaphus appears to be less specialized than that of Rana and Xenopus, contrary to what is generally believed for the lasttwo genera. Bufo, particularly and Bombina have undergone less specialization.

[发布机构] Stellenbosch University