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 



J 'c*l£*L*pfis<^-cta 



Scm^c^^Co. 



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 Cf. E. W. MacBride, " Echinodermata " in Cambridge Natural 

 History, vol. i., 1906. 



