. "The membrane surrounding the endoplasmic reticulum (ER). The endoplasmic reticulum is an extensive network of membrane tubules, vesicles and flattened cisternae (sac-like structures) found throughout the eukaryotic cell, especially those responsible for the production of hormones and other secretory products." . . "Endoplasmic reticulum membrane" . . . . "Endoplasmic reticulum membrane" .