PHYLUM CHORDATA 



397 



to secrete a digestive fluid similar to that produced by the liver 

 in the vertebrates. The intestine leads directly to the anus (an). 



FIG. 343. Diagram of the anatomy of Amphioxus. A, anterior, 

 B, posterior part, an, anus ; atr, atrium ; air 1 , its posterior prolongation ; 

 alrp, atriopore ; br, brain ; br.cl, branchial clefts ; brf, brown funnel ; 

 br.sep.i, br.sep.2, branchial lamellae ; br.r.i, br.r.2, branchial rods ; caud.f, 

 caudal fin; cent.c, central canal; cir, cirri; coel, coelom; dors.f, dorsal fin; 

 dors.f.r, dorsal fin-ray; en coe, cerebral vesicle; e,sp, eye spot; gon, gonad; 

 int, intestine ; Ir, liver ; mth, mouth ; myom, myotomes ; nch, notochord ; 

 nph, -nephridia; olf.p, olfactory pit; or.f.hd, oral hood; ph, pharynx; 

 sk, skeleton of oral hood and cirri (dotted); sp.cd, spinal cord; vent.f, ventral 

 fin; vent.f. r, ventral fin-ray; vl, velum; vl.t, velar tentacles. (From the 

 Cambridge Natural History, after Parker and Haswell.) 



RESPIRATORY SYSTEM. The pharynx (Fig. 343, ph; Fig. 

 342) is attached dorsally and hangs down into a cavity called 

 the atrium (Figs. 342-343, atr.). The atrium is not the ccelom 



