EABLY FOEMS OF THE INTESTINAL CANAL. 



327 



the gill-openings, which appear directly behind it on the 

 intestine. The front portion of the intestine has thus 



Fig. 280. — A simple Gliding Worm (Bhdbdoccelitm) m, mouth; sd, throat, 

 epithelimn ; sm, throat m.usole-mass ; d, etomaoh-intestine ; nc, renal ducts ; 

 /, ciliated outer-skin ; rmi, openings of the latter ; au, eye ; na, nose-pit. 



Fig. 281. — Strabture of an Ascidian (seen from the left side, as in Plate 

 XI. Pig. 14). The dorsal side is turned toward the right, the ventral side to 

 the left ; the mouth-opening (0) is above ; at the opposite, tail end, the 

 ascidian has become adherent. The gill-intestine (br), perforated by many 

 openings, extends into the stomach-intestine. The terminal intestine 

 opens through the anus (a) into the gill-cavity (cl), from which the excre- 

 ment is passed out with the respirated water through the gill-pore, or cloacal 

 opening (a') ; m, mantle. (After Gegenbaur.) 



