Observations on the substructure of flagellar fibres

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Abstract
The substructure of the outer and central fibres of the flagella of Trichonympha and other flagellates has been examined by electron microscopy, using negatively-stained material. Periodicities revealed in the micrographs have been analysed by studying the optical diffraction patterns obtained from them. Outer and central fibres appear to be essentially similar in sub-structure and are made up of a number of longitudinal filaments which form the wall of the hollow fibres. The filaments are 40–50 Å apart, centre to centre, and are beaded, the beads (or subunits) giving rise to an axial repeat along the filaments of 40 Å and a basic surface lattice of 40 × 50 Å. In collapsed or disintegrating fibres no other substructural features are usually visible. In intact fibres, however, additional longitudinal periodicities are apparent. An 80-Å spacing is prominent, and there is commonly also a strong 160-Å repeat. These appear to be orders of a fundamental 480-Å period. The long spacings are thought to arise as departures in the arrangement of the subunits from the simple 40 × 50 Å lattice, the perturbations probably occurring both radially and in the plane of the surface of the fibre. In the central fibres additional material is present, spaced at 160 Å and probably corresponding to the central sheath previously described from sectioned material. Observations on the arms of the outer fibres are described.