78 



SUBCELLULAR PARTICLES 



Fig. 8. Guinea pig pancreas. The micrograph shows the lumen (Ini) of an acinus surrounded 

 by the apical poles of 3 exocrine cells. Microvilli (long arrows), in cross or oblique section, 

 appear against the dense background of the discharged zymogen that fills the lumen. The limit- 

 ing membrane and the content of the zymogen granule marked Si appear in continuity with 

 the Cell membrane (short tirrotvs) and the luminal content respectively. It is assumetl that this 

 granule was fixed while emptying its contents into the lumen. Another zymogen granule (22) 

 discharges through the intermediary of 21. Other zymogen granules, still far from the cell mem- 

 brane, are marked ss and Zi. A few 'empty' vesicles, most of them smooth -surfaced (ss), can be 

 seen among the zymogen granules. A centriole (c) appears close to the luminal surface of one 

 of the cells. X 45,000. 



