Further observations on the glomerular root of the vertebrate kidney.

IN the kidneys of a wide variety of animals the second convoluted tubule is applied to the root of the glomerulus of the same nephron (Text-fig, i). Here the tubular cells are aggregated to form the macula densa. In these cells the Golgi element lies on the side of the nucleus opposite to that on which it lies in the rest of the tubule (McManus, 1943, 1944). The tubule is set into the angle between the afferent and efferent arterioles of the glomerulus (Text-fig. 2A). Rotation of the plane of section through 90 produces the appearance shown in Textfig. 2B. The arteriolar cells in this region are known in a variety of species to possess granules in their cytoplasm. These relationships become established at a very early stage in embryonic development. In the human foetus, and in every other embryo examined from fishes upqranular cells