tensions (annular tubules) which project into the nucleus and out into 

 the cytoplasm. Projections or blebs from the nuclear membrane (Figure 

 4-3) and the delamination of segments of it into the cytoplasm has also 

 been described. The association of electron-dense granules with the outer 



r; 



/ 



Figure 4-4. Electron Micrograph Showing Parts of Two Nuclei in a Bi- 

 nucleate, Acinar Cell of Rat Pancreas. Small, electron-dense cytoplasmic 

 particles are shown associated with the membrane elements of the endo- 

 plasmic reticulum and the outer membrane of the nuclear envelope. The 

 appearance of the outer nuclear membrane and its associated particles makes 

 it indistinguishable essentially from the rough-surfaced membranes of the 

 endoplasmic reticulum. A pore in one nuclear envelope is marked by an 

 arrow. (From Watson, M. L., 1955. "The Nuclear Envelope. Its Structure 

 and Relation to Cytoplasmic Membranes," J. Biophys. Biochem. Cytol., 1, 

 Fig. 5, Plate 73.) 



layer of the nuclear envelope (Figure 4-4) and continuity between this 

 layer and certain elements of the endoplasmic reticulum have been 

 observed in both plant and animal cells (Figure 4-5). The morphological 

 similarity and apparent continuity between the nuclear envelope and 



STRUCTURE AND FUNCTION OF THE NUCLEUS / 77 



