n6 



CEPHALOCHORDATA 



CHAP. 



epithelial cells (see Fig. 72, p. 118), some of which bear sensory 

 processes, while others have a striated cuticular border. There 

 is no general ciliation of the surface in the adult. 



The true mouth is a small pore at the bottom of a large 

 vestibule (the stomodaeum), placed at the anterior end of the 



inl 



FlQ. 71. Diagram of the anatomy of Amphioxus. A, anterior ; B, posterior part. 

 an, Anus ; atr, atrium ; atr', its posterior prolongation ; atrp, atriopore ; br, brain ; 

 br.cl, branchial clefts ; br.f, brown funnel ; br.sep.l, primary, br.sep.2, secondary 

 branchial lamella ; br.r.1, primary, br.r.2, secondary branchial rod ; ca-iid.f, caudal 

 fin ; cent.c, central canal ; mr, cirri ; coel, coelom ; dors.f, dorsal fin ; dm-c.f.r, dorsal 

 fin-ray ; en.coe, cerebral vesicle ; e.sp, eye-spot ; gon, gonad : int, intestine ; lr, 

 liver ; mth, mouth ; myom, myotomes ; nch, notochord ; nph, nephridia ; olf.p, 

 olfactory pit ; or.f.hd, oral hood ; ph, pharynx ; sk, skeleton of oral liood and cirri 

 (dotted) ; sp.cd, spinal cord ; vent.f, ventral fin ; vent.f.r, ventral fin-ray ; vl, velum ; 

 vl.t, velar tentacles. (From Parker and Haswell.) 



ventral surface (Figs. 70 and 71), and formed by the " oral hood," 

 which may be a prolongation forwards of the atrial or meta- 

 pleural folds at each side. The edges of the oral hood bear 1 2 to 

 20 pairs of cirri (Fig. 70, cir} or ciliated tentacles (strengthened 

 by skeletal rods), which form a sensory fringe around the open- 

 ing. The anus (Figs. 70 and 71, an), is asymmetrical, being 



