[Ontogeny of the pronephros and mesonephros in the South African clawed frog, Xenopus laevis Daudin, with special reference to the appearance and movement of the renin-immunopositive cells].

Development of the pronephros and mesonephros of Xenopus laevis was morphologically studied in the larvae immediately after hatch (stage 35/36) to the end of metamorphosis (stage 66) together with the appearance of renin-immunopositive cells. The pronephros consisted of 3 pairs of pronephric tubules at stage 35/36 and became functional at stage 37/38 with the opening of the pronephric ducts to the cloaca. It increased thereafter in volume, but became degenerative at stage 56, lost a part of the pronephric ducts at stage 60, and completely disappeared at stage 64. The mesonephros displayed its anlage at stage 42, and gained the immature renal corpuscles at stage 48. At stage 49, it was equipped with the matured nephrons. The mesonephric tubules differentiated into the neck, proximal, intermediate and distal parts. The collecting tubules and ducts were also observed at this stage. At stage 56, a part of the mesonephric tubules degenerated and were displaced by newly formed tubules. Reorganization of the mesonephros was not completed at the end of metamorphosis. Renin-immunopositive cells did not appear in the pronephros, but were observed at the diverging part of the renal artery from the dorsal aorta, and in the walls of arteries and afferent arterioles within the mesonephros in a low frequency of appearance.