A highly specific adenosine triphosphatase has been found to be localized in the contractile apparatus of vorticellids. It is most prominent in the cilia as well as in the myonemes which course the latitudes and longitudes of the cell and spiral in the flat peristome. The stalk displays more activity in the spasmoneme sheath than in the spasmoneme itself. The spasmoneme canal appears negative. A delicate fiber coils around the outside of the stalk in a helix. All these structures may be seen in the living protozoan by phasecontrast microscopy.