. Electron microscopy; proceedings of the Stockholm Conference, September, 1956. Electron microscopy. 148 B. A. AFZELIUS. Fig. I. The two RNA-containing bodies of microscopic dimensions in the egg cytoplasm can be compared in this picture. A portion of a "yolk nucleus" with a-cytomembranes enclosing a few mitochondria is seen at the right and two triangular heavy bodies to the left of this inclusion. The picture is from the sea urchin species Styungy/ocentroriis droehacliiensis. Magnification â 30,000. chondria were not or very faintly stained by this technique. Another cell componen
. Electron microscopy; proceedings of the Stockholm Conference, September, 1956. Electron microscopy. 148 B. A. AFZELIUS. Fig. I. The two RNA-containing bodies of microscopic dimensions in the egg cytoplasm can be compared in this picture. A portion of a "yolk nucleus" with a-cytomembranes enclosing a few mitochondria is seen at the right and two triangular heavy bodies to the left of this inclusion. The picture is from the sea urchin species Styungy/ocentroriis droehacliiensis. Magnification â 30,000. chondria were not or very faintly stained by this technique. Another cell component that stained with the RNA-specific stains was found occasionally in some oocytes of Swedish sea urchins and regularly in the oocytes of the species Strongylocentrotus droebachien- sis. This particle can be described as an elliptical body consisting of concentric membranes which often enclose a particle resembling a yolk granule or a few mitochondria. The total diameter is 5 /< or less. When centrifuged, these bodies go to the clear layer. They are sometimes called "yolk nuclei", which is not a particularly happy name as this term has been used for different structures in different oocyte types and as they have probably nothing to do with yolk synthesis. Electron microscopical observations.âTwo of the RNA-containing structures described above were recognized with certainty in the electron micro- scope on ultra-thin sections; the "yolk nuclei" of the oocytes and the heavy bodies of the mature egg. In the "yolk nucleus", whose membranous struc- ture is vaguely discernible with the light microscope, the individual membranes were seen to have a thickness of 60 A and to be associated with granules approximately 150 A in diameter. The membranes, like those of the exocrine pancreatic cells (20) were apparently arranged in pairs, with the granules located on their outer surfaces. The yolk granules and mitochondria that were typically enclosed by thes
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