Text-book of comparative anatomy . layer which contains theFIG. , after skeleton tbere is a thjn tesselated epithelium, in ruicckcl. -1 which case the body would consist of three layers —an outer ectodermal layer, an inner endodermal epithelium, and an intermediate mesodermal layer of connective tissue. Those sponges, which are essentially of the same degree of organisation as the Olynthus, are called A scones. A higher degree of organisation is attained when the body wallbecomes thicker and cylindrical tubes or pouches arranged closetogether penetrate into the thickened Avail radi
Text-book of comparative anatomy . layer which contains theFIG. , after skeleton tbere is a thjn tesselated epithelium, in ruicckcl. -1 which case the body would consist of three layers —an outer ectodermal layer, an inner endodermal epithelium, and an intermediate mesodermal layer of connective tissue. Those sponges, which are essentially of the same degree of organisation as the Olynthus, are called A scones. A higher degree of organisation is attained when the body wallbecomes thicker and cylindrical tubes or pouches arranged closetogether penetrate into the thickened Avail radially round the centralcavity (Fig. 58). The outer surface of the sponge is then often raisedin numerous cones over these radial tubes. The radial tubes are linedwith collar epithelium, while the epithelium of the central or gastralcavity is changed into a pavement epithelium. The outer poresin this case lead first into the radial tubes, from these into the centralcavity, and thence through the oseulum to the exterior. II PORIFERA 63 In most sponges, however, the canal system is more collar epithelium is limited to numerous so-called ciliatedchambers, which are sac-like, and generally liescattered in the much thickened mesoderm ofthe body wall (Fig. 59, gk). The pores of theouter surfaces of the body lead into much-branched canals of varying width, Avhich arelined with tesselated epithelium; these, asafferent canals, enter the ciliated canals of varying width, which oftenunite into larger canals, lead out of thechambers as efferent canals into the variouslyshaped central cavity, which again opens out-ward by means of an osculum. Such formsare known as Leucones. The movement of the flagella of the collarepithelium maintains a constant stream of waterthrough the canal system of the sponges. Thewater enters by the pores, passes through thecanal system, and flows out again through theosculum. The canal system may vary extraordinarily in det
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectanatomycomparative
