A transmission electron micrograph shows part of an acinar cell from the parotid salivary gland of a rat. These cells make the enzyme salivary amylase and secrete it into the ducts of the gland. The image is printed at a magnification of ×8000. Features visible in the image: • a large, rounded body bounded by a double membrane with pores, containing a darker, densely stained patch; • the base of the cell packed with many parallel membranes arranged in flattened layers, their outer surfaces dotted with tiny dark granules; • a stack of curved, flattened membrane sacs near the centre of the cell, with small round membrane-bound bodies budding from its edges; • towards the top (the side facing the duct) dozens of large, round, dark-staining membrane-bound granules; • several sausage-shaped organelles, each with a smooth outer membrane and an inner membrane folded into shelves — the one labelled X is the largest of these; • one of the large round dark granules is labelled Y; • the whole cell is enclosed by a single thin boundary line.