CHORD ATA. 135 



Phylum VI. CHORDATA. 



Coelomate animals with the neural and haemal surfaces dorsal and 

 ventral respectively. At some stage or other a cellular supporting rod, 

 the notochord, underlies the central nervous system for part or all of its 

 extent, and the pharynx is perforated by two or more gill-slits. 



The term Vertebrata is often applied in a wide sense to this phylum. All 

 other animals can then be lumped together under the name Invertcbrata. 



Subphylum A. Hemichorda. 



Chordata with a short notochord mainly situated in the prsestomium. 

 Balanoglossus, a worm-like marine form with prseoral contractile pro- 

 boscis, numerous paired gill-slits, and a branchial skeleton. Central 

 nervous system closely connected with the skin, and heart dorsal to noto- 

 chord. Mouth ventral, anus terminal. Body-cavity an enterocrele. Tor- 

 naria larva, presenting resemblances to Echinoderms, or Bateson's larva 

 with posterior ciliated ring. Generally placed near the Echinoderms in 

 a special group, Enteropneusta. 



Cephalodiscus and Rhabdoplenra are generally placed in the Poly- 

 zoa, as a sub-group Pterobranchia. Two gill-slits and a small notochord 

 have been found in the former. 



