Acinar cells of parotid salivary glands are intended to synthesize and secrete a large amount of proteins. The well-developed synthesizing machinery is a feature of these cells; it means, first of all, well-developed rough endoplasmic reticulum. Since it occupies a considerable part of the cytoplasm, the reticulum is also called ergastoplasm ("operating cytoplasm"). Cisterns of the ergastoplasm are rather numerous and well-arranged in the intracellular space. These flat and elongated bags are generally situated concentrically around the nucleus and separated by some narrow cytosol-filled splits. The cytoplasmic surface of cistern-forming RER membranes is almost entirely covered by attached ribosomes #1, #2. On transverse sections, these ribosomes look like rows of small dense corpuscles that are divided by slit intervals.