HOMOLOGY, 



17 



m a process of the moutli-iii volution which becomes " con- 

 stricted off." But he recognizes that the bhnd anterior end 

 of the alimentary canal — which he terms "throat" — is in 

 close contact with the " pituitary involution." This " invo- 

 lution becomes longer and dilated terminally, while the 

 passage connecting it with the mouth becomes narrower 

 and narrower, and is finally reduced to a solid cord, which 

 in its turn disappears. The remaining vesicle then becomes 

 divided into lobes, and connects itself closely with the in- 

 fundibulum" *. 



In higher Vertebrates the deuto- or pseudo-pharynx (figs, 

 1, 2, 4, s), extending to the parts ultimately modified as a pitui- 

 tary body or hypophysis with its onward and neurad exten- 

 sions — the infundibulum, third ventricle, and pineal produc- 

 tion — constitutes therewith the modified canal which traverses 

 the interspace between the homologues of the Invertebrate 



hsemoesophageal " (fig. 3, 6) and " neuroesophageal " 

 (fig. 3, 3) brain-masses — in Vertebrates the fore brain and 

 following brain-parts. In other words, from the neural side 

 of the embryonal or primary buccal cavity a communication 

 (figs. 1-4, 7, 8) is more or less carried on toward the surface 

 from the part where what is a diverticulum from the primi- 

 tive closed oesophagus (fig. 5, 8') seems to be seeking, as it 

 were, its outlet at the neural aspect of the body above a wide 

 interspace (fig. 4, 5) now separating the rudiment of the fore 

 brain (e) from those of the raid (4) and hind (3) brains. 

 . In all Invertebrates with appreciable homologues of these 

 divisions of the Vertebrate brain, the neural mouth (fig. 3, 7) 

 is opened at this part, the primordial attempt to attain it in 

 the Vertebrates is fulfilled, and the communication of such 



* ' Monograph on the Development of Elasmobraneh Fishes/ 1878, 

 p. 190. 



C 



