Philosophers through the ages have made the astute observation that life, in its many aspects, appears to be continuously moving. All things in the universe, from the cosmic to the atomic level, exhibit some form of movement. Getting down to earth, the capacity to move is also an essential feature of the biological world. Movement was in fact synonymous with life at the time that Antony van Leeuwenhoek made the first simple microscope (seventeenth century). Using his primitive instrument he observed micro-organisms. which he called 'animalcules', swimming through a drop of water, and...