224 ARTHUR WILLEY. 



Enteropneusta, tlie authors have neglected the opportunity of 

 pointing an interesting and instructive analogy. 



What the Urochorda are to the Cephalochorda, such are the 

 Pterobranchia to the Enteropneusta. 



The perpetual domination of the notochord in classification 

 constitutes a noteworthy example of the manner in which 

 zoological knowledge moves along well-worn grooves. There 

 is strong reason to suppose that the gill-clefts have the priority 

 of the notochord, or at least equal antiquity with it; and if 

 this supposition should prove to be correct in principle, there 

 ought to be some indication of it in the classificatory system. 



I have treated this subject in some detail in a memoir on the 

 Enteropneusta collected by me in the South Pacific, which will 

 shortly be published;' and ihe following is a simplified form 

 of the table of classification there constructed. 



PHYLUM BRANCHIOTEEMA, n.n. 



I. HEMICHORDA, Bateson, 1884. 

 Class 1. Pterobranchia, Lankester, 1885. 

 Class 2. Enteropneusta, Gegenbaur, 1870. 



II. PKOTOCHORDA, Balfour, 1882. 

 Class 1. Urochorda, Lankester, 1877. 

 Class 2. Cephalochorda, Lankester, 1877. 



III. VERTEBRATA/ Lamarck and Cuvier. 

 Class 1. AcRANiA, Haeckel, 1866. 

 Class 2. Craniota, Haeckel, 1866. 



In the above system the group containing Amphioxus 

 appears under two different names, Cephalochorda and 

 Acrania. I see no objection to this procedure, nor any other 

 way out of the difficulty. 



' In Part, iii of A. Willey's 'Zooloj^ical Results' (Canibriclgc University 

 I'resb). 



- Vertebrata = liolocliorda, Gadow, IS'JS. 



