TEM micrographs of flat-embedded flagella from WT C. reinhardtii cells containing IFT trains. (a) Low-magnification view of longitudinally sectioned flagella (arrowheads) and cell bodies (cb). (b) Four cross sections of WT flagella containing IFT trains. The arrows show some cross-sectioned IFT trains (IFT), located between the flagellar membrane and the axoneme and close to outer dynein arms (ODA). Arrowheads indicate the links between the IFT trains and B tubule of MT doublets. (c) A longitudinal section of a flat-embedded flagellum from a WT cell. The section is cut through the central core of the flagellum at the level of the central pair apparatus (cp). Two of the nine MT doublets (md) are visible beside the central pair. Underneath the flagellar membrane (m), IFT trains with two different morphologies are present: short trains are labeled with white arrowheads, whereas longer trains are marked with black arrowheads, and their extremities delineated with short black lines.