Endoplasmic reticulum

The endoplasmic reticulum (ER) is a type of organelle in eukaryotic cells that forms an interconnected network of flattened, membrane-enclosed sacs or tube-like structures known as cisternae. The membranes of the ER are continuous with the outer nuclear membrane.

Quotes

 * The evidence already discussed stresses the role played by the endoplasmic reticulum and the Golgi complex in the production and processing of secretory proteins. The stress put on secretion leads, however, to an apparent impasse. Since every eukaryotic cell possesses both an endoplasmic reticulum and a Golgi complex, it follows that all eukaryotic cells secrete proteins or that the organs of the secretory pathway have additional, perhaps more general and more important functions than secretion, which have been ignored or are still unknown.
 * George Emil Palade, Nobel Prize Lecture (1974)