Outlines of zoology . a. Fig. 103.—Diagrammatic longitudinal sectionof a Nemertean (Amphiporus laciijioreus),dorsal view.—After MIntosh. ^.^•, Proboscis pore; 6., brain giving off tbe lateralnerve-cords («.); ^o,, oesophageal pocket: p., pro-boscis lying within its sheath;. st., stilet of proboscis ;m., retractor muscles of proboscis ; ^., gut shown inoutline at the sides of the proboscis; e., the threemain longitudinal blood vessels, which unite bothanteriorly and posteriorly. 198 UNSEGMENTED WORMS. General Account of Nemertea In appearance most Nemertines are ribbon- or thread-like, and thec
Outlines of zoology . a. Fig. 103.—Diagrammatic longitudinal sectionof a Nemertean (Amphiporus laciijioreus),dorsal view.—After MIntosh. ^.^•, Proboscis pore; 6., brain giving off tbe lateralnerve-cords («.); ^o,, oesophageal pocket: p., pro-boscis lying within its sheath;. st., stilet of proboscis ;m., retractor muscles of proboscis ; ^., gut shown inoutline at the sides of the proboscis; e., the threemain longitudinal blood vessels, which unite bothanteriorly and posteriorly. 198 UNSEGMENTED WORMS. General Account of Nemertea In appearance most Nemertines are ribbon- or thread-like, and thecross-section is generally a flattened cylinder. They show a greaterdiversity of size than any other worms,—from a Lineus, 12 or morefeet in length (25 metres has been recorded for an extended Lineuslongissimus), to the pelagic Pelagonemertes, which is under an are often bright, and tend to resemble those of the sur-roundings. The ectoderm is covered with numerous short cilia, and Fig. 104.—Transverse section of the Nemertean Drepanophorus —After Burger. , Dorsal or proboscis nerve; ,, proboscis sheath; , probosciscavity; , sac of proboscis cavity; dorso-ventral muscles;, circular muscles ; /.»;., longitudinal muscles; /.«., lateral nervewith brariches; A, parenchyma; ^., gut; /.z*.., lateral blood vessel,.beside which lies an excretory vessel; H.^., excretory pore ; , dorsalblood vessel; £p. epidermis. many of its cells are also glandular, secreting the mucus, whichoften^forms a tube around the animal, or is exuded in movement. Beneaththe epidermis there is a parenchyma, consisting in part of connectivetissue, and often in part gelatinous. The body is remarkably con-tractile, and in some cases the spasms result in breakage. The muscles-are circular and longitudinal, and often also diagonal. The fibres arestriped. In the adult there is no distinct ccelom, the space between;the gut and the body
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Keywords: ., bookcentury1900, bookdecade1910, bookidcu3192, booksubjectzoology
