Figure 3: Vesicle cell and duct from amber vesicle of Aplysia californica. (a) Enlarged portion of vesicle cell from Figure 2(f) with sack-like invaginations (arrows) of the cell membrane which is also closely associated with rough endoplasmic reticulum cisternae (arrow heads). (b) Duct lumen filled with protein. L, lumen; n, nucleus. Scale bars: (a) = 0.5 μm; (b) = 2 μm.