As cytokinesis progresses, FtsZ filaments keep assembling and growing, soon forming a complete ring of long, overlapping filaments around the full circumference of the cell. This drives further constriction more or less uniformly. In this Caulobacter crescentus cell in a later stage of division, you can see many FtsZ filaments lined up in cross-section–the dots on both sides of the division plane. If we rotate the cell around, you can see filaments extending on both sides as far as the membrane is visible. (See the note on the previous page about why we cannot trace the membrane and filaments all the way around.) They will continue to pull the membrane inward, and direct cell wall to be built behind it, until cytokinesis is complete.
