SUMMARY: In sunlight dark-ground microscopy the flagella of a packet of motile sarcina appear as a smooth tail. The tails often stiffen into helices of two different wavelengths, one being twice as long as the other. The short and the long wavelengths are identical in Sarcina ureea and S. agilis. This phenomenon of two wavelengths, one twice as long as the other, was also found, though less frequently, in certain other bacteria. Otherwise the wavelengths of the flagella of these bacteria appeared specific.