Fig. 10. A thin section through the base of the bristle cell from an isolated thorax that had been treated for two hours with cytochalasin D before fixation. The thorax was dissected from a 41-hour pupa. By 43 hours, bundle disassembly in the controls had not yet occurred. In the cytoplasm surrounding the nucleus (N) are numerous small bundles (a) each containing about 50 filaments. One of the bundles is depicted at high magnification in (b). The lines indicate the 12-nm period attributable to the crosslink fascin.