. Cassell's natural history. Animals; Animal behavior. gi-adually disappear fvom the exterior of the calyx ; though in one rare genus and in most Stalked Crinoids they are visible beneath the radials, alternating with them in position, and cutting them off more or less completely from the top stem-joint. Jointed on to the first radials, and attached to them by muscles, are the five second radials (Fig. 22, R,), each in its turn bearing a third or axillary radial (r,;). The outer face of this is roof-shaped, and bears tlie lowest joints (b) of two arms, which may oi- may not fork again. Immedia
. Cassell's natural history. Animals; Animal behavior. gi-adually disappear fvom the exterior of the calyx ; though in one rare genus and in most Stalked Crinoids they are visible beneath the radials, alternating with them in position, and cutting them off more or less completely from the top stem-joint. Jointed on to the first radials, and attached to them by muscles, are the five second radials (Fig. 22, R,), each in its turn bearing a third or axillary radial (r,;). The outer face of this is roof-shaped, and bears tlie lowest joints (b) of two arms, which may oi- may not fork again. Immediately beneath the ciliated am- bulacral or food-groove of each arm and pinnule lies a nervous band (Fig. 21, n), and deeper still, a blood-vessel {h), just as in the groove on tlie under-side of a Starfish arm (Fig. 9, H, h). Beneath the blood-vessel is the water-vessel (Fig. 21, ««),• wliich gives off side branches to the tentacles (t). These are delicate tubular organs, which are situated at the sides of the food-groove, and correspond to the tube-feet of the Starfish (Fig. 9, t). Not being required for locomotion, tliey are essentially breathing organs. Tlie water-vessels of the arms unite into five trunks which communicate, like those of the Starfish arms, with a ring-shaped vessel (Fig. 20, wr), situated in the lip around the mouth. There is, however, no such direct communica- tion between this vessel and the external water as is efi'ected by the stone-canal or water-tube of the Echinozoa. But water is able to ent«- the body-cavity by innimierable small tubular openings in its walls, the water-pores (Fig. 20, IV p). These are lined by cilia, all working in- wards ; and, on the other hand, the water-vas- cular ring is in free communica- tion with the body-cavity by means of delicate ciliated tubuli— the water-tubes (Fig. 20, wt), 9" the open ends of svhich hang down into it, and thus Fig. 20. establish an in- direct communi- 'jnmts' cation between JJ,";,-; t
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Keywords: ., bookcentury1800, bookdecade1890, booksubjecta, booksubjectanimals
