THE ENTBROPNEUSTA. 31 



the Enteropneusta among the Chordata. I wouldj therefore, 

 tentatively suggest the following table : 



C h o r d at a. — Hemichordata (Enteropneusta) . 



Urochorda (Ascidians). 



Cephalochorda (Amphioxus). 



Vertebrata. 

 It is not now proposed to enter into a more detailed dis- 

 cussion of the morphology of the group, or of the light which 

 an acceptance of this suggestion throws on the origin of the 

 Chordata. A fuller examination of these points is reserved for 

 a subsequent occasion. 



It may nevertheless be advisable to point out that since, 

 according to Spengel, the tissue of the " water vessel" of Tor- 

 naria forms the lining of the proboscis cavity of B. minutus, 

 this " water vessel" is therefore the same structure as the 

 anterior body cavity in the form just described. If, then, the 

 " water vessel" of Tornaria is comparable to the " water 

 vessel" of Bipinnaria, which has a similarly asymmetrical de- 

 velopment upon the left hand side of the body, which view has 

 been held by all previous observers, it would therefore appear 

 to follow that the water vessel of Bipinnaria is prima facie 

 comparable with the asymmetrical anterior body cavity of 

 Amphioxus. 



Later Development and Comparative Account of 

 the Organs in the various Species. 



The species which I have examined are the following : 

 B. Kowalevskii (Alex. Agassiz.) (Coast of North America) . 

 B. Brooksii, n. sp. (ditto). 

 B. minutus (Kowalevsky.) (Bay of Naples). 

 B. salmoneus (Giard.) (lies de Glenans, off South Coast 

 of Britany). 



B. Robinii (Giard.) (ditto). 



B. Kowalevskii differs from all the others in having — 



(1) a relatively long proboscis ; 



(2) no hepatic sacculations ; 



