Figure 171 from Chapter 5 (Endoplasmic Reticulum) of 'The Cell, 2nd Ed.' by Don W. Fawcett M.D. Electron micrograph of rough endoplasmic reticulum (RER) in two adjacent acinar cells from the pancreas of the small brown bat, Myotis lucifugus. The surface membranes for the two cells are closely apposed and slightly thicker than the membranes associated with the ER. While free ribosomes are apparent between the plasma membrane and the ER, the ribosomes are separated from the inner border of the plasma membrane by about 10 nm (arrows). In contrast, the membrane associated with the ER is studded with adherent ribosomes. A PDF copy of the accompanying chapter is available on the ASCB’s BioEDUCATE website.