11 
of Edinburgh, Session 1884 - 85 . 
untenable are — first, the hypophysis is developed in most cases from 
the epiblast of the actual mouth, and not from the hypoblast ; and, 
second (a reason which I believe has never before been definitely 
stated), that the original mouth did not open on what is now the 
dorsal surface above the nervous system, but on the floor of the 
cerebral vesicles, which is part of the primitive body surface. The 
conditions required for the rudiment of the primitive mouth are 
satisfied completely, and it seems to me exclusively, by the infundi- 
bulum. This latter structure is in the embryo a diverticulum from 
the floor of the first cerebral vesicle, which comes into contact with 
the anterior eqd of the mesenteron. In Miss Johnson’s paper “On 
the Newt ” a pit is described at the front end of the primitive blasto- 
pore, at the bottom of ydiich pit epiblast and hypoblast are fused. 
The writer believes that this pit becomes the actual mouth. I think 
therp is little doubt that if she had traced the fate of the pit in 
question she would have found that it became the infundibulum. 
I know that in herring embryos, in front of the notochord, the 
neurochord conies into contact with the hypoblast. Dohrn* has 
come to the conclusion that the hypophysis cerebri is the rudiment 
of a praeoral pair of gill-clefts. If this conclusion hold good, it gives 
support to my view of the primitive mouth, for a pair of gill-clefts 
would have opened into the original oesophagus, and therefore might 
very well in actual Vertebrates come into connection with the 
rudiment of the primitive mouth, as the pituitary body does with 
the infundibulum. As for the pineal gland, it does not concern 
the question in the least ; it is connected with the closing of the 
medullary canal, and is of comparatively small importance in the 
present discussion. 
The Notochord . — Ever since the notochord was first described in 
some embryos as originating from the hypoblast, morphologists 
have considered that it must phylogenetically be derived from the 
intestine. Now, comparative anatomy shows that this supposition 
is untenable. The dorsal aorta in the fish is homologous with the 
subintestinal vessel in the Chaetopod : if the notochord had been 
derived from the intestine, it would lie between the aorta and the 
intestine — its actual position is between the aorta and the neuro- 
chord. It is not consistent with the principles of evolution to 
* Milt, der Zool. Station zu Neapel, Bd. iv. Heft. 1. 
