Three-dimensional views of a model flagllum at the end of a computation of flagellar movement. The upper view shows the flagellum at normal diameter. In the lower view, the diameter has been expanded four-fold. The red and blue bands identify the regions between axonemal outer doublets occupied by dyneins on doublets #4 and #8, respectively. These bands demonstrate the internal rotation, or writhe, of the axoneme caused by its bending in three dimensions. See Figure 3 of the article by Brokaw in Cell Motility and the Cytoskeleton, 53(2) 2002.