. Cytology. Cytology. through this structure of relatively large units by diffusion, as in the case of the oocyte nucleus which appears to be freely permeable to molecules up to the size of proteins. Also in the light of what is known regarding ultrastructure it is not impossible that its permeable properties are subject to considerable variation. A number of electron microscopy. Figure 4-3. Electron Micrograph of Drosophila Salivary Gland Cell Showing Outpocketings (Blebs) of the Nuclear Membrane. Note association of highly differentiated chromosomal material with the developing blebs. Approx
. Cytology. Cytology. through this structure of relatively large units by diffusion, as in the case of the oocyte nucleus which appears to be freely permeable to molecules up to the size of proteins. Also in the light of what is known regarding ultrastructure it is not impossible that its permeable properties are subject to considerable variation. A number of electron microscopy. Figure 4-3. Electron Micrograph of Drosophila Salivary Gland Cell Showing Outpocketings (Blebs) of the Nuclear Membrane. Note association of highly differentiated chromosomal material with the developing blebs. Approximately 45,000x. (From Gay, H., 1956. "Chromosome-Nuclear Membrane-Cytoplasmic Interrelations in Drosophila," J. Biophys. Biochem. CytoL, 2, Fig. 8, Plate 137. Courtesy of Dr. Helen Gay, Carnegie Institute of Washington.) studies have shown the nuclear envelope to be a double-layered structure containing pores formed by continuities between the outer and inner layers of the envelope (Figure 4-2), In certain cells, a thin membrane extending across the pores and separating the contents of the nucleus from those of the cytoplasm has been observed. The presence of annuli or rings of electron-dense granules surrounding the pores of the envelope has also been reported. These annuli appear to be associated with ex- 76 / CHAPTER 4. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Wilson, G. B. (George Bernard), 1914-; Morrison, John H. (John Herbert), 1927-. New York, Reinhold
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