WITH NOTES OX THE WEST INDIAN SPECIES. 



297 



metamorphosis of Tornaria and that he, like his successors Bateson, Morgan (loc. cit.), 

 MacBride 1 and others, believed in the special though remote genetic relationship of the 

 Enteropneusta and Echinoderma ; the name is also useful as a reminder of the supposed 

 bilateral ancestry of the Echinoderms. 



The other collective name which I have suggested, viz. Hydrotrema, will be 

 justified in the sequel. 



With regard to the introduction of the name, Branchiotrema, I will say that 

 there is just as much or as little need for this addition to our terminology as there 

 was for Huxley's Pharyngopneusta. Moreover, assuming that the knowledge of these 

 creatures which has accumulated during the last thirty years or so, is not illusory, 

 I think that the conception contained in this term, namely, that gill-slits have the 

 priority of the notochord, will turn out to be well-grounded. 



A table, such as the one given here, brings out the dual or overlapping pro- 

 pensities of the various groups in a way which is not possible in an ordinary 

 classification. 



MKMORIA TECHNICA 

 Relating to the Chordate Series of Animals. 



Hydrotrema 



Branchiotrema 



Bilateralia 

 Metschnikoff 1881 



Echinoderma 

 Klein 1734 



Hemichorda 

 Bateson 1884 



Pharyngopneusta 

 Huxley 1877 



Chordoma 

 Haeckel 1866 



Pterobranchia Enteropneusta 

 Lankester 1885 Gegenbaur 1870 



Protochorda 

 Balfour 1882 



Vertebra ta s 

 Lamarck — 1800 — Cuvier 



Urochorda 

 Lankester 1877 



Cephalochorda 



Lankester 1877 



= Acrania 

 Haeckel 1866 



Craniota 

 Haeckel 1866 



The theory for which I shall proceed to point out the evidence may be briefly 

 stated as follows : — The gonads and gill-slits were primarily unlimited in number and 

 coextensive in distribution, the gonads having a zonary disposition and the gill-slits 

 occupying the interzonal depressions. The primary function of the gill-slits was the 

 oxygenation of the gonads, their secondary function being the respiration of the individual. 



Perhaps it will be best to deal with the evidence categorically. 



1 E. W. MacBride, "The development of Asterina gibbosa." Q. J. 31. S., Vol. 38, 1896. 



2 Holochorda of Gadow and Masterman. (H. Gadow, A Classification of Vertebrata, London, 1898. A. T. 

 Masterman, "On the Diplochorda," Quart. Journ. Micro. Sci., Vol. xl. 1897.) 



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