. Electron microscopy; proceedings of the Stockholm Conference, September, 1956 . Fig. 1. Photomontage of electron micrographs of an early stage of a developing, rat renal glomerulus, with prospective endothelial cells but without capillaries, or capillary structures. {A) Bowman's capsular epithelium, and thin capsular basement membrane characteristic of these early stages. {B) Initial capsular space, seemingly developed by separation of the two epithelial layers. (C) Prospective podocytes, or Bowman's visceral epithelial layer. (D) Prominent cell surface mem- branes between the outermost pros
. Electron microscopy; proceedings of the Stockholm Conference, September, 1956 . Fig. 1. Photomontage of electron micrographs of an early stage of a developing, rat renal glomerulus, with prospective endothelial cells but without capillaries, or capillary structures. {A) Bowman's capsular epithelium, and thin capsular basement membrane characteristic of these early stages. {B) Initial capsular space, seemingly developed by separation of the two epithelial layers. (C) Prospective podocytes, or Bowman's visceral epithelial layer. (D) Prominent cell surface mem- branes between the outermost prospective endothelial cells and the prospective podocytes. Especially noteworthy are the absence of a capillary basement membrane, and the short, broad extensions of podocytic cytoplasm between the prospec- tive endothelial cells. (£") These extensions may play an important role in the organizing of prospective endothelial cells into the capillary system characteristic of the glomerulus. (F) Two cells of an immature arteriole. (C) Capsular connection with tubule. Note within the mass of prospective endothelial cells, the mitotic figure, ni. and the precocious erythrocytes, as f, and the complete absence of formed capillaries. Osmium fixed. Magnification 2065. spective endothelial and podocytic cells were seen bounding the narrow space which in a later stage would be occupied by lamina densa. During these early stages of development, the basement membrane of Bowman's capsule appeared very tenuous. It had much the appearance of a fused, thickened membrane on the external surface of the prospective parietal epithelium. Flattening of the outermost concentric layer of cells and the concomi- tant initial definite appearance of a limited capsular space was the next recognizable advance in the dif- ferentiation of the Malpighian corpuscle. Pronounced mitotic activity of the prospective endothelial cells characterized this stage (fig. i). The flattening of the prospective parietal c
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