Branches can change their topological order. The figure shows four images from a time-lapse series at 0 (A), 60 (B), 145 (C), and 222 (D) min. The second-order process labeled 1 in A has generated a third-order branch labeled 2 in B. Thearrows in B–D point to the bifurcation point. In C, process 1 has retracted to the bifurcation point, so that it now appears that processes1 and 2 are part of a single, bent process. In D, a new, higher-order branch (3) has formed on the original third-order branch. Anterior is to the left. Scale bar forA–D, 25 μm.