. The Cambridge natural history. Zoology. 586 ECHINODERMATA CRINOIDEA in the centre of its five chambers a median pocket grows down into the centro-dorsal, along the side of which is an extension of the genital stolon. In the arms the mesentery separating the extensions of the oral and aboral coelom persists; the oral ex- tension consists of two parallel canals called " subtentacular" (Fig. 267, ), whilst the aboral space is termed the " coeliac " canal (Fig. 267, ). In the tip of the pinnule, that is to say at the extremity of a ramification of the arm, the coeliac a
. The Cambridge natural history. Zoology. 586 ECHINODERMATA CRINOIDEA in the centre of its five chambers a median pocket grows down into the centro-dorsal, along the side of which is an extension of the genital stolon. In the arms the mesentery separating the extensions of the oral and aboral coelom persists; the oral ex- tension consists of two parallel canals called " subtentacular" (Fig. 267, ), whilst the aboral space is termed the " coeliac " canal (Fig. 267, ). In the tip of the pinnule, that is to say at the extremity of a ramification of the arm, the coeliac and sub- tentacular canals communicate. As portions of the lining of both canals are ciliated, a circulation of the coelomic fluid is thus. Fig. 267.—Diagrammatic transverse section of arm of Antedon. To compare it with tlie section of an Ophiuroid arm it is inverted from its natural position. 6r, Brachial ossicle ; , coeliac canal; , covering plate ; , genital canal; , genital rachis; , dorsal nerve- cord ; , ventral nerve-cord ; pod^ po- dium ; , subtent- acular cacal ; , radial water-vessel. pod. kept up. The genital stolon gives rise at the level of the remnant of the horizontal mesentery in the disc to a circular genital rachis, whence cords pass down the arms in the tissue separating subtentacular and coeliac canals (Fig. 267, ). Each cord is contained in a special tube, the " genital canal," which is probably developed in the same way as the aboral sinus of the Eleutherozoa, as a special sheltering outgrowth of the coelom (Fig. 267, ). In the pinnule the rachis swells out into a genital organ, from which a short duct is developed when the organ is mature. The eggs are large (3 mm. in diameter), and adhere for a considerable period of their development to the Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1895
