SIGNIFICANCE OF KUPFFER’s VESICLE. 
9 
the primitive ancestor of the Vertebrates had a central nervous 
system which had not separated from the epiblast in which it 
was developed. As Mr. Sedgwick points out, the nervous system 
in the living Vertebrates is continuous with the epiblast, and in 
this respect the Vertebrate is on a par with the Ccelenterate 
and the Echinoderm. It follows, then, that the limiting surface 
of the neural canal in Vertebrates is part of the original surface 
of the body. Now, there is one fact in the organization of a 
worm which requires to be taken most seriously into account 
in forming an idea of its transformation into a Vertebrate. 
This fact is the perioesophageal nerve-collar. We may sup- 
pose — we must suppose — that, although in the worm -like 
ancestor of the Vertebrate the nerve-cords were continuous 
with the epiblast, these cords diverged to enclose the mouth, 
and met again in front of it just as they do in a modern 
annelid. In the Vertebrate, then, we must find a rudiment of 
the original mouth within the neural canal. I believe I 
have hit upon this rudiment : it is the infundibulum of the 
brain. The infundibulum is a deep depression in the floor of 
the neural canal which comes into the closest relation with the 
hypoblast. I am not referring in the faintest way to the 
hypophysis or pituitary body, which seems, according to recent 
researches, to be derived from the epiblast of the actual mouth. 
But the infundibulum in a Vertebrate embryo is, I believe, 
actually in contact with the hypoblast in front of the notochord. 
Elsewhere, along the back of the embryo, the neurochord is 
separated from the hypoblast by the notochord; the notochord 
ceases at the infundibulum. I fully accept all that Mr. 
Sedgwick says about tbe elongated blastopore along the Verte- 
brate back, and I would point out that Mr. Sedgwick’s view 
makes the back of the Vertebrate homologous with the ventral 
face of the worm, just as does the Dohrnian hypothesis. But 
according to Mr. Sedgwick, a supraoral portion of the nervous 
system in the worm has disappeared in the Vertebrate (and in 
Balanoglossus) ; and the present mouth and anus in the Verte- 
brate are not secondary new structures but the primitive ones. 
This I strenuously oppose. If we look at certain Teleostean 
