Embryonic development of kidneys in viviparous <em>Typhlonectes compressicauda</em> (Amphibia, Gymnophiona)
The embryonic development of organs within Gymnophiona is still poorly known. In Typhlonectes compressicauda, a caecilian amphibian expressing a derived viviparous reproductive mode, development can be divided into 34 stages and is characterized by a metamorphosis occurring between stages 30 and 33. At stages 18-19, Wolffian ducts appear in the anterior part of the embryo. At stage 23, a pair of pronephric kidneys is clearly visible with several nephrostomes that empty into the coelomic cavity. At stage 30, pronephroi that were observed at the level of the second and fifth vertebrae are now observed between the 24th and 28th vertebrae. At this stage, several mesonephric tubules appear between the 29th and 32nd vertebrae, and mesonephric tissue is observed in the posterior part of the body. At stage 31, pronephroi begin to disappear. The mesonephroi have now proximal and distal tubules. At stages 32-33, two mesonephroi are visible as a pair of lengthened layers, representing the definitive kidneys.