(A). Scanning electron microscopy image of a T. brucei procyclic cell. Inset shows cross-section TEM image. (B) Resin-embedded samples exhibit a range of orientations, cross-section (CS) and longitudinal-section (LS) are shown. (C) Frozen-hydrated samples in LS orientation show the axoneme (AX) and paraflagellar rod (PFR) side by side. (D) CS view from tomogram of stained samples (slice thickness≈50nm). Outer doublet microtubules (OD), radial spokes (S), outer arm dyneins (OAD), inner arm dyneins (IAD), central pair microtubules (CP) and nexin links (N) are indicated. Ax-PFR Connections are visible. The proximal (P), intermediate (I) and distal (D) PFR zones are indicated on both CS (D) and LS (E–F) views. LS views from tomograms of stained (E) and frozen (F) samples show repeating structures along the flagellum (≈3nm thick). Compasses (E,F) show sample orientation with respect to axoneme (A), PFR (P), base (B), tip (T) and left (L) and right (R) sides (viewed from flagellum base to tip). Scale bars 1 µm (A), 100nm (B–C, E–F) and 50nm (D).