HOLOTHUROIDEA. 



257 



29 



.-24 



without any marked line of separation, into the intestine. The 

 intestine after a short course backwards turns forwards and 

 extends to near the front end of the body (F,'g. 181), where 

 it again bends 

 backwards to 

 pass to the 

 r e c t u m o r 

 cloaca, which 

 opens by the 

 anus at the 

 hind end of 

 the body. The 

 alimentary 

 canal is con- 

 nected to the 

 body wall 

 along its whole 

 length by a 

 mesentery 

 which is 

 mainly de- 

 rived fro m 

 the dorsal 

 mesentery of 

 the larva. It 

 is t h e r e f ore 

 larval - dorsal, 

 but in the 

 adult its at- 

 tachment is 

 different in 

 the different 

 parts of the 

 tube. The 

 first reach of 

 the alimen- 

 tary canal, 

 consisting of 

 oesophagus, 

 stomach and 



JZ III 



Fin. 181. One of the Aspidoehirotae opened and viewed from the 

 left side, diagrammatic (from Leuckart's Wandtafeln), The 

 body wall has been cut through just to the left of the dorsal 

 middle line. The mouth is at the upper end and surrounded by 

 tentacles. The tentacular ampullae are not represented. 1 radial 

 vessel leaving the water-vascular ring 2 ; 3 blood-vascular ring ; 

 4 polian vesicle ; 5 oesophagus ; 6 ventral blood-vessel of the 

 intestine ; 7 vessel connecting the ventral blood-vessel of the first 

 and second part of the intestine ; 8 second part of the intestine ; 

 !>, 10 radial longitudinal muscle ; 11 left respiratory tree ; 12 

 dorsal blood-vessel of intestine ; 13 circular muscles of body-wall ; 

 li cuvierian organs ; 15 cloaca ; 16 anus ; 17 radial muscles of 

 cloaca : IS cut edge of body-wall ; 19 right respiratory tree ; 

 20 posterior edge of the dorsal mesentery ; 21 median ventral 

 longitudinal muscles : 22 third part of intestine : 23 first part of 

 intestine ; 24 gonad ; 21 so-called internal madreporites of two 

 stone-canals ; 26 dnrsal mesentery ; 27 genital duct ; 2S inter- 

 racliaL 29 radial piece of the calcareous ring ; 30 genital opening. 



S 



