72 DIVERGENCE AND PARALLELISM 



in phylogeny seems more firmly established 

 than the pelmatozoic ancestry of the Echino- 

 derms (star-fishes, sea-urchins, etc.), nor than 

 the bilaterally symmetrical ancestry of the 

 Pelmatozoa, the former deduction largely result- 

 ing from their paleontology, the latter confirmed 

 by their embryology. 1 



As for the Vertebrata, not all of them possess 

 vertebrae, but all have a notochord. The term 



/n. 



FIG. 4. Parallel divisions of Vertebrata. 



Protochordata, with the subsidiary terms Uro- 

 chordata (for the Tunicata or Ascidians) and 

 Cephalochordata (for the Acrania or Amphioxus), 

 was introduced by Balfour in his "Comparative 

 Embryology" in 1882. Subsequently in 1884 

 Bateson suggested the additional term Hemi- 

 chordata for the Enteropneusta (" Balano- 



1 C/.E.W. MacBride, " Echinodermata " in Cambridge Natural 

 History, vol. i., 1906. 



