GILLS. 



247 



forwards above the latter, and joins the mouth-cavity at the velum. 

 The anterior part of the oesophagus of the adult is thus a neo- 

 morph : it is at first solid, but becomes hollowed secondarily. 



eg 



FIG. 199. Amphioxiis lanceolcdus, x 



(From Gegenbaur, after Quatrefages.) 



a, aperture of month, surrounded by cirrhi ; b, anus ; c, atrial pore ; d, branchial sac ; 

 e, stomach-like section of the intestine ; /, csecal process (? liver) ; g, intestine ; 

 7i, general body-cavity ; i, notochord, and under it the aorta ; k, aortic 

 arches ; I, aortic heart ; m, swellings on the branchial arteries ; n, contractile 

 postcaval vein ; 0, contractile portal vein. 



Thus two canals pass backwards from the mouth, a ventral 

 branchial or respiratory tube, and a dorsal oesophagus 

 (Fig. 200, B). 



