146 PKOF. OWEN OF THE HOMOLOGY 



In the view of the homologous surfaces of the Invertebrate 

 and Vertebrate bodies as determined by that which may happen 

 to be the upper surface in horizontal station and progression, 

 which surface is accordingly termed "dorsal," the opposite or 

 under surface being "ventral," the chief nerve-mass in the Arti- 

 culate (fig. 3, 6), called " cerveau" by Cavier, poses as the homo- 

 logue of the brain in the Vertebrate ; and not only so, but being 

 the only part of the central nerve-mass which is "dorsal" in 

 position, or "above" the alimentary canal, it might be entitled, 

 according to the above homology of the body-surfaces, to be the 

 homologue of the entire central nerve-mass (my " myelencepha- 

 lon") in Vertebrates, which is also " dorsal ;" while the ganglionic 

 nerve-cords in Articulates would be in the opposite homological 

 category. 



Accordingly the accomplished Anatomical Professor at Hei- 

 delberg, in logical concord with such determination of homo- 

 logous surfaces, holds the so-called " superoesophageal ganglion " 

 of the Articulate to be, or to represent, the whole myelen- 

 cephalous tract in the Vertebrate. With Gregenbaur*, as with 

 Cuvier, the "spinal cord" is therefore peculiar to Vertebrates, 

 being "dorsal" in position ; it bears no true homology with the 

 so-called " ventral" cords, whether ganglionic or not, in Inverte- 

 brates. 



Dohrnf, while admitting the homology or equivalency o£ the 

 superoesophageal ganglions, suboesophageal ganglions, and sub- 

 or ventral cords therefrom continued, whether ganglionic or 

 otherwise, in Annelids and Arthropods, with themyelencephalous 

 tract in Vertebrates, notwithstanding the opposite sides of the 

 body which they seem to hold, has recourse to ideal ancestral 

 forms in order to reconcile the diiferences as to relative position 

 shown by the actual or modern subjects J. 



My contention is that the true grounds for determining the 

 homology in question are not the positions of the body which may 

 be assumed by the living animal, but the relative positions to such 

 body of the central parts of the nervous and vascular systems, 

 which relations I have expressed by the terms "neural" and 

 " haemal." The convenience of these terms or signs is exempli- 



* ' Grundriss der Tergleichenden Anatomie,' 8vo, p. 264. 

 t ' Ursprung der Wirbelthiere,' &c. 



I I concur with the remarks by Balfour, loc. cit. p. 167, on Dohrn's hypo- 

 thesis, and deem any other objection superfluous. 



