194 



BRANCH CHORDATA 



SUB-PHYLUM AND CLASS III. ACRA'NIA OR AMPHIOXUS 



This is a small fish-like chordate 2 or 

 3 inches in length. 



Its shape is one found for the first time, 

 that of narrow ventral and dorsal sur- 

 faces and deep lateral surfaces. It is 

 pointed at both ends. It falls on its side 

 when not in motion. 



It is marine and lies buried in the 

 clean sand along warm seacoasts, with 

 its ciliated lips protruding. The currents 

 produced by the cilia bring fresh water 

 with its oxygen to the gills. Small organ- 

 isms are also thus furnished for food. 



The Am'phiox'us (Fig. 156) has no 

 limbs, no skull, no well-differentiated 

 brain, and no heart, but it has a noto- 

 chord (a smooth cylindric rod lying above 

 the alimentary tube), a nerve cord dorsal 

 to the notochord, numerous gill-slits, 

 and aif alimentary tube. The sexes are 

 separate. 



The alimentary tube is a straight tube 

 consisting of mouth, pharynx, and in- 

 testine. On the right side of the pharynx 

 is a blind pouch, the so-called liver. 



The circulatory system consists of a dor- 

 sal arterial trunk and a ventral venous 

 trunk connected by lateral arches. The 

 blood is colorless. 



Fig. 156. Amphiox'us lanceola'tus : a. Anus; 

 aw, eye; b, ventral muscles; c, body cavity; ch, 

 notochord; d, intestine; do and du, dorsal and 

 ventral walls of intestine; /, fin-seam; h, skin; 

 k, gills; ka, gill-artery; Ib, liver; lv, liver-vein; 

 TO 1 , brain vesicle; m*, spinal marrow; ing, 

 stomach; o, mouth; p, ventral pore; r, dorsal 

 muscle; s, tail fin; t, t, aorta; v, intestinal vein; z, boundary between gill 

 intestine and stomach intestine; y, hypobranchial groove. (After Hackel.) 



