Transmission electron micrograph of guinea pig pancreas membrane fractionations. Field is from the bottom quarter of the pellet . At this level the preparation consists primarily of large single sheets of cell membranes often associated with parallel sheets of basement membrane which indicate that they are coming from the basal region of the exocrine cells. Image corresponds to Figure 11a from J. Cell. Biol. 49:109-129, 1971. Image made available by James D. Jamieson and the Department of Cell Biology, Yale University School of Medicine.