In order to study all stages of DVs in the same cell we used a protocol of sequentially exposing cells to different sizes of latex beads interspersed with washes: for example, 3 minutes in 0.1µm beads, wash 3 min, 3 minutes in 0.3µm beads, wash 3 min, 3 minutes in 0.6µm beads, wash 3 min, 3 minutes in 0.8µm beads, wash 3 min and finally 3 minutes in 1.1µm beads followed by fixing the cells. Thus the 1.1, 0.8, 0.6, 0.3 and 0.1µm bead-containing vacuoles will be 0-3 min, 6-9 min, 12-15 min, 18-21 min and 24-27 minutes old, respectively. The electron micrograph shown here was of a DV-II that was surrounded with docked secondary lysosomes. Secondary lysosomes only recognize and dock at the DV-II membrane. They do not dock with DV-I or DV-III vacuoles. TEM taken on 2/27/81 by R. Allen with Hitachi HU11A operating at 75kV. Neg. 7,000X. Bar = 0.5µm.