. The Cambridge natural history. Zoology. 5 84 ECHINODERMATA CRINOIDEA mouth, from which radial cords are given off which run under the ambulacral grooves (Fig. 266, ). The fibres of this nervous system are, as in Asteroidea, immediately beneath the bases of the ectoderm cells. A large band of fibres is given off to each podium, which is covered with minute elevations, each with pointed sense-hairs in the centre. As the animal grows, another nervous system makes its appear- ance, which is developed from the coelomic wall, the cells of pod wvr â ,' gen r ,
. The Cambridge natural history. Zoology. 5 84 ECHINODERMATA CRINOIDEA mouth, from which radial cords are given off which run under the ambulacral grooves (Fig. 266, ). The fibres of this nervous system are, as in Asteroidea, immediately beneath the bases of the ectoderm cells. A large band of fibres is given off to each podium, which is covered with minute elevations, each with pointed sense-hairs in the centre. As the animal grows, another nervous system makes its appear- ance, which is developed from the coelomic wall, the cells of pod wvr â ,' gen r , ^â^i ,. Fig. 266.âDiagrammatic longitudinal section through one arm and the opposite inter- radius of Antedon. ax, Central canal of oentro-dorsal, with prolongation of genital stolon; B, rosette, consisting of coalesced basals ; £r^, Br\ B'l^, Br^, the first four brachial ossicles; chamb, chambered organ ; coel. coe, coelomic canal of arm; gen. coe, genital canal of arm ; , genital rachis ; , genital stolon ; , madreporic pores ; , longitudinal muscle ; , dorsal radial nerve ; , ventral radial nerve ; , pore-canal; pod, podium ; £}-£?, 1st to 3rd radials ; , stone-canal ; , sub-tentacular canal of arm ; , radial water-vessel. certain tracts of which multiply and bud off ganglion cells from which the fibres grow out. This " aboral nervous system," as it is called, has its centre in the "chambered organ" (Fig. 266, chamb), which is embedded in the centro-dorsal ossicle, and is roofed over by a plate called the " ; This represents the five coalesced " basals," a ring of plates which in other forms alternate with the lowest radials, and it intervenes between these and the centro-dorsal. The chambered organ consists of a ring of five vesicles, which have originated as pouches of the aboral coelom (Fig. 266, chamh). The walls of these vesicles develop ne
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1895
