26 



CONARIO-HYPOPHYSIAL TRACT. 



tebrate becomes " hsemastomous," the Invertebrate remains 

 " neurostomous." 



At the embryonal stage of the higher subclass at which 

 the primary mouth was continued across the brain, the 

 " Unity of Plan " between the Vertebrate and Invertebrate 

 animal was exemplified ; and that " unity " is, in the main, 

 preserved under the recognition of the neural and haemal 

 aspects of the body, as shown in figs. 2 and 3, representing 

 the Articulate and Vertebrate types. 



In the view of the homologous surfaces of the Invertebrate 

 and Vertebrate bodies as determined by that which may 

 happen to be the upper suiface in horizontal station and pro- 

 gression, which surface is accordingly termed " dorsal," the 

 opposite or under surface being " ventral," the chief nerve- 

 mass in the Articulate (tig. 3, e), called cerveau " by 

 Cuvier, poses as the homologue 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 alimen- 

 tary canal, it might be entitled, according to the above 

 hom^ology of the body-surfaces, to be the homologue of the 

 entire central nerve-mass (my " myelencephalon ") in Verte- 

 brates, which is also " dorsal ;" while the ganglionic nerve- 

 cords in Articulates would be in the opposite homological 

 category. 



Accordingly the accomplished Anatomical Professor at 

 Heidelberg, in logical concord with such determination of 

 homologous surfaces, holds the so-called " supraoesophageal 

 ganglion " of the Articulate to be, or to represent, the whole 

 myelencephalous tract in the Vertebrate. With Gegenbaur, 

 as with Cuvier, the " spinal cord " is therefore pecuhar to 

 Vertebrates, being "dorsal" in position; it bears no true 

 homology with the so-called " ventral " cords, whether gan- 

 glionic or not, in Invertebrates. 



