Figures 377 (upper) and 378 (lower) from Chapter 15 (Cytoplasmic Inclusions) of 'The Cell, 2nd Ed.' by Don W. Fawcett M.D. Comparison between the human pancreatic acinar cell (upper) and guinea pig pancreatic cell (lower) reveals species differences in size and density of secretory vesicles in the same cell type. The zymogen granules in the human acinar cell are more dense, or osmiophilic than those of the guinea pig. Upper image by Susumo Ito and Arthur Like; lower from R. Bolender, J. Cell Biol. 61:269-87, 1974. A PDF copy of the accompanying chapter is available on the ASCB’s BioEDUCATE website.