Flagellar propulsion

In this JEB Classics paper, Sir James Gray and G. J. Hancock explained how spermatozoa are propelled by flagellar bending waves (Gray and Hancock, 1955). This paper was a lasting success because it provided an easy-to-understand solution to a complicated hydrodynamic problem, and because it provided a quantitative prediction of the swimming speed that was almost identical to the swimming speed measured in Gray's accompanying paper on the movement of sea urchin spermatozoa (Gray, 1955).