SEPTA-The body cavity of earthworm is a true coelom which lies between the body wall and the alimentary canal.It is lined by the coelomic epithelium derived from the mesoderm.The coelom is partitioned into a series of coelomic chambers by transverse intersegmental septa. The septa are absent in the first four segments.The first septum lying between segment 4and 5 is thin and membranous.The next five septa are thick and muscular.Septum between 8/9 or9/10 is lacking. The first nine septa up to septum 13/14 are without perforations.The remaining septa begining from septum 14/15 are perforated by numerous sphinctered apertures,through which adjacent coelomic chambers maintain continuity.
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