Up to the present time nematodes have been considered to be pseudocoelomatic organisms (Turk, 1903; Goldschmidt, 1906; Chitwood and Chitwood, 1950). These authors failed to observe true membranes completely surrounding the organs and separating them from the body cavity and were only able to detect net-like tissues arising from mesenchymatous cells covering or partially supporting the organs (pseudocoelomatic membranes and mesenteries) and series of isolated cells (coelomocytes) (Chitwood and Chitwood, 1950). Observations by Grimaldi De Zio and Morone De Lucia in 1974 revealed the presence of a true membrane completely enveloping the gonads of species of Longidorus (Micoletzky) Filipjev and Xiphinema Cobb (Dorylaimida: Longidoridae). Further studies with the electron microscope, carried out in the Laboratorio di Nematologia agraria, have confirmed these observations and have led to the discovery of a similar structure along the digestive tract and lining the somatic muscles.
