Fig. 7. Solid modules separate longitudinally into a series of subbundles. All of these figures come from 54- and 55-hour old pupae. Panels (a and b) show thin transverse sections through a bristle. The chitinous exoskeleton of the bristle is being deposited outside the plasma membrane surrounding the bristle. Located at the top of panel (a) are three bundles (arrows) illustrated at higher magnification in (b). Each bundle has separated into two subbundles. The dots in the bundles are the actin filaments cut in cross section. Panel (c) shows a section through a module with a flat basal end and a pointed apical end that is splitting into two subbundles. The 12-nm period attributable to the cross-bridge fascin is indicated on this micrograph by the three bars. This period is best seen by looking across the bundle from its side. Panel (d) shows a deeper split of a bundle into two subbundles. Panel (e) shows two tandem modules splitting into a series of subbundles. At least one subbundle remains associated with the plasma membrane.

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