The anatomy and histology of the kidney of A. pusillus were studied by means of resin infusions, corrosion casts and standard histochcmicat procedures using quantitative measurements where possible. Keywords: Anterior vena cava, Azygos vein, Blood vascular system, Cetaceans, Electrophoresis system, Elucidating basic physiological phenomena, Glomerulometrics, Hematoxylin, Interrencular collagenous connective tissue, Magnesium counts, Osmolality, Pinnipeds, Plasma protein, Relative medullary thicknesses, Renculate kidney and Unilobar rodent kidney.