Fig. 1. (A) Electron micrograph and accompanying diagram of axonemal transverse section following the induction of microtubule sliding. The axoneme is oriented as viewed, proximal to distal and based on the doublet (Db) numbering system of Hoops and Witman (Hoops and Witman, 1983). Db3 has slid away from the axoneme leaving doublet 2 on the dynein exposed edge of the active area (arrow). (B) Diagram of the six possible sliding patterns observed following ATP-induced microtubule sliding. The associated central apparatuses are not meant to imply that only transverse sections with a specific central apparatus orientation are included in the analysis. The numbers indicate the number of doublet microtubules that remain associated with the central apparatus. (C) Flagella as viewed looking towards the cell body. The arrows indicate the direction of the beat plane during the effective stroke.