Figure 1.

(A) Transverse section of flagellar axoneme. The outer and inner dynein arms (ODA, IDA) and radial spokes (RS) are attached to the outer doublet microtubules. The central apparatus is enlarged and offset. Central pair projections are labeled according to Mitchell and Sale (10). (B) Electron micrograph and accompanying diagram, axoneme transverse section after microtubule sliding. The C1 and C2 microtubules of the central pair are labeled. The arrow defines the orientation of the central pair. The point at which the arrow intersects the circumference of the doublets is indicated by a dot on the accompanying diagram. The position of active microtubule sliding includes the area lightly shaded. The inactive area includes the remainder of the axoneme (dark shading).