. Electron microscopy; proceedings of the Stockholm Conference, September, 1956 . Fig. 2. Electron micrograph of tiie mid-bulb region of tiie follicle showing early cell contacts and (probably) contact spread. The cells of the matrix contain many mitochondria, many agranular vesicles and large numbers of the dense particles thought to contain ribonucleic acid (3). There are none of the specialised intracellular inclusions which appear later at higher levels in the follicle. The surfaces of the cells are very convoluted and intercellular gaps are common. Numerous small finger shaped pseudopods
. Electron microscopy; proceedings of the Stockholm Conference, September, 1956 . Fig. 2. Electron micrograph of tiie mid-bulb region of tiie follicle showing early cell contacts and (probably) contact spread. The cells of the matrix contain many mitochondria, many agranular vesicles and large numbers of the dense particles thought to contain ribonucleic acid (3). There are none of the specialised intracellular inclusions which appear later at higher levels in the follicle. The surfaces of the cells are very convoluted and intercellular gaps are common. Numerous small finger shaped pseudopods project from the surfaces and often penetrate deeply into neighbouring cells. Close contact between the cells is limited to a few small areas where the two plasma membranes arc parallel and separated by a distance of about 120- 150 A. We conclude therefore that the surface mem- branes of the undifTerentiated cells are flexible and in active motion. Their adhesion is small and contact is both temporary and limited in area. The space between the membranes at these "adhesive contacts" is not by any means empty. A material of rather poor electron scattering power is observed both between the closely opposed surfaces and also spread out over the immediately adjacent surfaces. We sup- pose that this material is the cement responsible for the adhesion of the surfaces. Very little can be deduced concerning its chemical nature. The very slight reaction with the osmium fixative suggests that it is not protein or lipid in nature, but that it might be polysaccharide. In view of the important role we shall assign to it in morphogenesis, it is most regrettable that more is not known. When the cells further along the follicle are ex- amined the importance of cell contacts becomes apparent (figure 2). The areas of contact spread and. in a /ipper-like fashion, draw the cells together with the result that intercellular gaps are closed and the surface convolutions are smoothed out (figu
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