The cells comprising the filaments are enclosed within a tube or extracellualr material referred to as a sheath. Typically, the sheath is transparent when viewed in wet mounts under the phase microscope. It appears much like a microscopic plastic tubule or pipe usually but not always containing cells. Ocassionally the sheath is so thin and closely associated with the cells that it cannot be readily discerned by phase microscopy. The addition of 95% ethanol to the wet mount may help its visualization. alternatively, it may be detected within the filament if there are gaps between cells. sheathes may appear yellow to dark brown owing to the depostion of iron and manganese oxides