18 



CONARIO-HTPOPI-IYSIAL TRACT. 



neural mouth with the alimentary canal is completed and 

 becomes the persistent gullet {ib. 7, lo). 



The proposition, therefore, which I now submit is, that 

 the conario-hypophysial tract in Vertebrates is the modified 

 homologue of the mouth and gullet of Invertebrates. That 

 the neur- or suboesophageal ganglion, or ganghonic masses, 

 or neural cords (fig. 3, 3, 5), constituting the centres whence 

 are derived and caudally continued the homologue of the 

 Vertebrate myelon (id. i), together with the part of the gullet 

 they encompass, are consequently the homologues of the parts 

 of the brain (fig. 2, 4, 3) posterior to the cerebrum (id. e) and 

 of the ventricle (fig. 4, 5) intervening between the upper 

 and lower ends — pineal {id. 7) and pituitary {id. s) — of the 

 conario-hypophysial tract. Thus, as it appears to me, is the 

 Uniti/ of Organization or Composition vindicated, though in a 

 transitory manner, between the Vertebrate and Invertebrate 

 brain-possessing animals. The foregoing developmental phe- 

 nomena have mainly guided me to a homological application 

 which, so far as my readings have extended, appears not to 

 have suggested itself. 



An obvious difference from the mature Vertebrate is the 

 greater relative proportion, in length, of the encephahc to the 

 myelonic divisions of the neural axis, in the early stages of 

 development, and the retention of such character in degrees 

 corresponding with the low position of species in the Verte- 

 brate subkingdom. It is conspicuously manifested by the 

 relative extent of the interspace dividing the fore brain from 

 the mid brain, depending chiefly on the functional relations 

 of the interposed ahmenfary canal in Invertebrates (fig. 3, 7-io). 

 The proposed homology appears to me to throw some welcome 

 light on the similar though transitory proportions of the same 

 interspace in the Vertebrate, even the Mammahan, embryo, 

 as exemphiied in fig. 4. And we now look with interest 



