The ammonia and urea excretion of different species of Amphibia during their development and metamorphosis

Abstract

The ammonia and urea excretion by different types of Amphibia (Rana temporaria, Bufo bufo bufo. Xenopus laevis Triturus vulgaris, T. cristatus and the axolotl, Siredon mexicanum) was followed from the embryonic stage through metamorphosis to the adult fully grown stage. Ammonia was the predominating nitrogenous waste product during the embryonic and larval stages of all spp. Urea predominated in the post-metamorphic stages of spp. which became terrestrial after metamorphosis, ammonia in the postmetamorphic excretion of X. laevis. the only completely aquatic sp. examined. The metamorphosis of the axolotl upon the admn. of thyroxine resulted in an increase in the amt. of urea excreted relative to ammonia. A similar change resulted when precocious metamorphosis of R. temporaria was induced by thyroid extract. The question of biochemical reversibility in evolution is discussed in relation to the nitrogenous excretion of X. laevis which has made a return to the aquatic environment.