Fig. 3. Membrane expansion occurs from a site near the furrow base. A suspension of carbon particles was pipetted over the surface of devitellinated cleaving embryo. A video time-lapse sequence recorded particle movement during new membrane expansion. (A-D) Frames from the sequence, captured at 125 second intervals. (E) Kymograph made by vertically reprojecting the region of the timelapse image stack indicated by dotted box in frame A. Small arrows (a-d) indicate times in the sequence corresponding to panels A-D, respectively. Based on the parallel trajectories indicated, particles near each other travel at nearly identical speeds. Because they do not drift apart, evidently little new membrane insertion occurs between them. Vertical scale bar, 250 µm. Horizontal scale bar, 5 minutes.