EARLY FORMS 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 (Rhabdoccelum) : m, mouth; sd, throat- 

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

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



FIG. 281. Structure of an Ascidian (seen from the left side, as in Plato 

 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 (br), perforated by many 

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

 opens through the anus (o) into the gill-cavity (cZ), from which the excre- 

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

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



