. Electron microscopy; proceedings of the Stockholm Conference, September, 1956 . Fig. 2. Photomontage of electron micrographs of a later stage in the development of the rat, renal glomerulus, demonstrat- ing the early formation of the lobular organization, and initial stages of capillary formation. These incompletely differen- tiated capillaries are characterized by a very limited and apparently discontinuous capillary lumen, and by large, connecting masses of still undiflerentiated endothelial cells, and by the presence of few differentiated endothelial cells. The capillary spaces appear to
. Electron microscopy; proceedings of the Stockholm Conference, September, 1956 . Fig. 2. Photomontage of electron micrographs of a later stage in the development of the rat, renal glomerulus, demonstrat- ing the early formation of the lobular organization, and initial stages of capillary formation. These incompletely differen- tiated capillaries are characterized by a very limited and apparently discontinuous capillary lumen, and by large, connecting masses of still undiflerentiated endothelial cells, and by the presence of few differentiated endothelial cells. The capillary spaces appear to develop by the expansion and subsequent fusion of intra-cytoplasmic spaces which develop within the differentiating endothelial cells. (A) Capsular epithelium, and basement membrane, still characteristically thin. {B) Much enlarged capsular space. (If invagination played an important role in glomerular formation, this space should be reduced, not enlarged.) (C) Maturing podocytes, developing discrete processes, pedicels and trabeculae, and greatly increasing in size. (D) The cell surface membrane of the podocyte, which folds to form the numerous pedicels and trabeculae, while the definitive capillary basement membrane forms in intimate relationship with the surface membrane of the endothelial cells. (£) Prospective and differentiated endothelial cells. (F) Maturing arteriole. (G) Connection with tubule. Magnification x 2025. and processes in prospective podocytes. The mature podocyte (2, 3) is characterized by an extensive and complex system of relatively large processes, the trabeculae, and numerous, minute, interdigitating, terminal processes, the pedicels (foot-processes) which arise bilaterally from more or less parallel trabeculae radiating from the central mass of each podocyte. Differentiating podocytes acquired first, short, relatively broad processes, like those in fig. 1, which appear to fit into irregular spaces between the peripheral prospective endothelial cells.
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