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STRUCTURE OF* VERTEBRATA 



directly functional, and have no associated gill-lamellce. The 

 heart is ventral. The eye begins its development as an out- 

 growth from the brain. 



General Classification of Phylum Chordata 



Class Hypostomata (extinct). 

 Class Cyclostomata (Round Mouths), without true jaws. 

 Myxine, hag-fish. Petromyzon, lamprey. 



Sub-Phylum Cephalochorda. — Amphi- 

 oxus or Lancelet. 



iSalpa type. 

 Sub-Phylum I Ascidian type (sea- 

 Urochorda or -| squirts). 

 TuNicATA. I Appendicularia (lar- 



l val type persistent). 



Surviving offshoots of ancestral Vertebrates. 



Phylum Hemichorda or Enteropneusta (offshoots of incipient Vertebrates ?). 



Balanoglossus, etc. ; probably Cephalodiscus ; possibly Rhabdoplciira. 



