98 



ZOOLOGY. 



a nervous cord to the eye at the end of the ray. It may be 

 discovered by pressing apart the ambulacral feet along the 

 median line of each arm. Fine nerves are sent off to each 

 sucker, passing through the opening between the calcareous 

 plates and extending to each ampulla, thus controlling the 

 movements of the ambulacral feet. 



Fig. 62. Longitudinal section through the body and one arm of Asterias vulgaris. 

 m, mouth; s, stomach; I, lobe of stomach extending into the arm; a, anus ; nr, ner- 

 vous ring ; n, radial nerve ; vr, water- vascular ring, sending a radial vessel (v) into the 

 arm ; mp, madreporic plate ; t , stone canal ; h, haemal canal ; ov, oviduct ; o, ovary ; 

 am, ampullae, the ambulacral feet projecting below ; b, cceca or liver. Drawn by 

 A. F. Gray, under author's direction. 



The mouth (Fig. 62, m) is capacious, opening by a short 

 oesophagus into a capacious stomach (Fig. 62, s) with thin 

 distensible walls, and sending a long lobe or sac (Fig. 62, /) 

 into the base of each arm ; each sac is bound down by two 

 retractor muscles attached to the median ridge lying be- 

 tween the two rows of water-sacs (ampullae, see also Fig. 63). 



Fig. 63. Diagram of the cross-section of an arm. A, of Asterias rubens ; B. of 

 opfiiura texturata ; , ambulacral feet ; j?', ampullae .; t, dermal tentacles ; w, nervous 

 ords w, ambulacral plates ; w, muscles ; a, ambulacral vein ; b, ventral plate ; c, tot- 

 al plates; d, dorsal plate ; &, calcified portion of the integument. After W Lance 

 from Gegenbaur. 



The stomach ends in a short intestine, the limits between 

 the two not distinctly seen. The intestine suddenly con- 

 tracts and ends in a minute rectum situated in an angle 

 between two of five fleshy ridges radiating from the centre 



