GOLDSCHMIDT S MONOGEAPH OF AMPHIOXIDES. 597 



tinalis which I have likened to a pveeoral lobe. I may be 

 allowed to remai-k that whether or not there has been any 

 objective confusion, there has at least been no nnconscious 

 mental confusion on my part on this particular point. 



The prasoral lobe or proboscis should, I suggest, be regarded 

 as an axial organ, forming part of the normal body-length, 

 neither dorsal nor ventral. The functional situs oris is 

 determined by special factors (such as its relation to the 

 anterior neurenteric canal in the Tunicate larva) and should 

 be considered on a basis of its own. The mouth may be 

 dorsal, ventral or lateral in actual position. That the prteoral 

 lobe is essentially axial is indicated by the manner and order 

 of its development in the embryos of Acraniates and Entero- 

 pneusta, and also in the regeneration of the proboscis of the 

 latter (see Dawydoff, " Ueber die Regeneration der Eichel 

 bei den Enteropneusten," ' Zool. Anz.,^xxv, 1902, pp. 551-6). 



In conclusion, as to the relation of the Acrania to the 

 Ascidians, Dr. Goldschmidt is of the opinion that the deve- 

 lopmental tendency leads from Amphioxides to Amphioxus, 

 and beyond this in a straight line to the Ascidians, whose 

 organisation appears to him to have arisen by degeneration 

 from the Acrania. In opposition to this theory I submit 

 that the Ascidians have degenerated from an extinct coelo- 

 mate perennichordate type, but not from a cephalochordate 

 type. 



When, however, Dr. Goldschmidt asserts that the capacity 

 which resides in the pharynx of Acrania, as illustrated in the 

 particular instance of Amphioxides, of forming a gill-slit 

 between the segments over a great region of the body, 

 indicates the original existence of very numerous primitive 

 gill-slits, and supports the theory of the primary poly- 

 tremism of Vertebrates, I am glad to say that I agree with 

 him heartily.^ 



September, 1906. 



1 Cf. A. Willey, "Euteropneusta from the South Pacific," 'Zoological 

 Results' (Cambridge University Press), part iii, 1899; and R. C. Punnett, 

 "The Enteropneusta," 'Eauna and Geography of tlie Maldive and Laccadive 

 Archipelagoes,' vol. ii, part 2, 1903, see p. 6G9. 



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