A treatise on zoology . ges in the separation of an axial eanal,exemplified by brachials of Ghsocrinits onnin-dactylus. 1 is youngest; 4, oldest, x (> diani. I02 THE CRINOIDEA called ambulacrals (Amb), which can open or close as occasiondemands (Fig. IX.). We may now trace the variousextensions of the Body Systems intothe Thecal Cavity. The food-grooves and associatedstructures, except the axial cord, passover the tegmen to the mouth, intowhich the food-grooves drive theirstreams of water. The mouth leadsinto a gut, which makes a dextral coildown to the bottom of the cup, andthen rises alon
A treatise on zoology . ges in the separation of an axial eanal,exemplified by brachials of Ghsocrinits onnin-dactylus. 1 is youngest; 4, oldest, x (> diani. I02 THE CRINOIDEA called ambulacrals (Amb), which can open or close as occasiondemands (Fig. IX.). We may now trace the variousextensions of the Body Systems intothe Thecal Cavity. The food-grooves and associatedstructures, except the axial cord, passover the tegmen to the mouth, intowhich the food-grooves drive theirstreams of water. The mouth leadsinto a gut, which makes a dextral coildown to the bottom of the cup, andthen rises along the side of the cup tothe anus; this system, then, is notaffected by radiate symmetrv (seeFig. YII. p. 9). The epithelial nerves on the floor p are supported onjside-plates or Qf the food-SrOOVeS alsO paSS tO theadambulacrals (.), between winch ^ . ^ • i t i are .seen notches for sacciiii (p. 137), mouth, where they join an epithelial X 15 diam. • j ridgethis oral ring, nerves passpaired subtentacular nerves. Fig. IX. Ambulacrals. 1, ventral view oftwo brachials of Gissocrinus sqvami-fer, with closed above and re-moved below, X 8 diam. 2, side viewof brachials of Antedon hattirurro,with open, exposing tentacles (/);c encircling the mouth; fromto the walls of the gut. Therun down to a subepithelial, circumoesophageal nerve-ring, below the oral nerve-ring. Fromthis ring proceeds, in each interradius, a pair of nerves whichinnervate the tegmen and the mesenteries of the body-cavity. Thisnerve-system is connected with the aboral nerve-system in a mannerexplained below. The radial pseudhaemal canals join a pseudhaemal ringround the oesophagus beneath the oral nerve-ring ; these structuresare hard to distinguish, and even in other classes, where they arebetter developed, their origin is not yet clear. There is, however,surrounding the oesophagus a lacunar plexus belonging to whatis generally called the blood-vascular system. The circumoeso-phageal ring is connected
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Keywords: ., bookcentury1900, bookdecade1900, bookpublishe, booksubjectzoology
