The excretory system, when present, typically is only visible as a cuticle-lined duct that opens through the body wall as a ventral pore (Fig. 1). Generally the excretory pore is slightly posterior to the nerve ring, in the region near the isthmus or basal bulb of the pharynx. The precise regulatory or secretory function of the excretory system is poorly understood, and it is likely to vary among taxa. Although difficult to see with the light microscope, in some nematodes the excretory duct leads to a large single gland, whereas in other nematodes it may include a complex of glands as well as one or two tubular channels that may nearly extend the length of the nematode.