Thin-section EM. Monopolar HeLa cells in pear (A) and furrow (B) stages by EM. Boxed regions in A and B are magnified in a–e. In both stages, bundled polarized microtubules terminated in the cytoplasm micrometers away from the membrane. The ends of many of these bundles were capped by electron-dense material (black arrows). The blebbing activities at the furrow-like cortex were high in pear stage but decreased significantly in furrow stage, especially in the furrow. Endoplasmic reticulum (white arrows) was polarized in a linear manner parallel to the polarized microtubules. Centrosomes (indicated by the white dashed circle) were observed in adjacent thin sections. Cytokinetic blebs on the opposite side of the furrow-like cortex are indicated with an asterisk.