A green helical organism is described which displays a new type of movement. The helix moves by growing at the anterior end and diminishing posteriorly; it does not rotate. Observations on the change in shape produced by dehydration show that the structure of the organism is markedly anisotropic. By analogy with other fibrous structures, it may be concluded that anisodiametric micells or molecules are orientated parallel to the long axis. It is pointed out how the growth and activity of the organism are related to this axis. The systematic position of the organism is discussed and its possible affinity with the Spirochaetoidea (Dobell) and Cyanophyceae considered.