Body cavity of Pheretima is a true coelom which lies between body wall and alimentary canal. It is lined by coelomic epithelium derived from mesoderm. Coelom is partitioned into a series of fcoelomic chambers by transverse intersegmental, septa. Each septum consists of a thin layer of interlacing muscle fibres, covered on both surfaces by coelomic epithelium. Septa are absent in first four segments. First septum, lying between segments 4 and 5, is thin and membranous. Next five septa are thick and muscular. All these six septa are cone-like, and run obliquely backwards from body wall to gut wall. There is a single septum between segments 8 and 10.