EARLY FORMS OF THE INrp:.-;TINAL CANAL. 



327 



tho gill-openings, which appear directly ]>ehind it on the 

 intestine. The front portion of the intestine has thus 



Fig. 280. — A simple Gliding Worm {Rhahdncce''u'm) m, mouth; sd, throat- 

 epithelium ; sm, throat muscle-mass ; d, stomach -intestine ; nc, renal ducts; 

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



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

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

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

 ascidian has become adherent. The gill-intestine (hr), 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.) 



