Nitrogenous Excretion by Embryos of the Viviparous Snake Thamnophis S. Sirtalis (L.)

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Abstract
Functional considerations of the placenta of saurian reptiles are limited virtually to assumptions based on known embryonic requirements and structural placental features (Weekes, 1935). It appeared that the nature of embryonic excretion might profitably be investigated in the garter snake whose young are born alive. The extreme solubility of urea, and the fact that the black snake embryo excretes only 20% of its nitrogenous waste as uric acid (Clark, 1953), suggest the possibility that embryos of a placental saurian reptile might pass urea and ammonium salts to the blood stream of the mother; whether some of the soluble nitrogenous excreta are eliminated through the placenta or whether all nitrogenous excreta are retained in the foetus and adnexa, the degree to which the embryo is dependent upon uric acid is of interest. Accordingly, assays of urea, ammonia and uric acid in the developing embryo were undertaken.

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