Abstract
Live spermatozoa of the Japanese quail were observed as they swam in highly viscous salines. Under these conditions, torsions of the flagellum were readily seen. The torsions had a characteristic magnitude (nominally 180 degrees) and pattern of incidence. As a cycle of bending propagated over it, each position on the flagellum experienced first a sinistral torsion and, later, a restoring dextral torsion. The two zones of torsion were each associated with bending; between them was a torsion-free zone that tended to be straight. The amount of interdoublet sliding needed to generate the torsions may be as little as 10 nm. These dynamic propagating torsions have been detected by following the angular displacements of individual (swollen) mitochondria lying adjacent to the axoneme. It is suggested that torque generation is a primary outcome when the unconstrained '9 + 2' axoneme is activated.