Figure 8.

Thin section cut through the barbed portion of a developing fish hook bristle tip similar to the one shown in Fig. 7 C, from a mutant containing six copies of the forked gene. (A) The main shaft of the bristle extends upwards. This section contains two actin filament bundles in longitudinal section (enlarged in C). As in Fig. 7, the barbed portion forms at nearly right angles to the shaft proper and contains eight membrane-associated actin filament bundles (enlarged in B) and numerous microtubules in a parallel array. (B) Higher magnification of two actin bundles cut in transverse section. Most significant is the filaments in the bundles are hexagonally packed albeit with gaps or holes in the bundles. (C) Longitudinal section through an actin bundle in the shaft. If this figure is viewed from the side we can easily discern the 12-nm period (black lines) due to the fascin cross-link.