of Edinburgh, Session 1884-85. 
171 
inflected, nor does the embryo ever extend to the edge of the 
blastoderm, as it does in Elasmobranchs and Teleosteans. In the 
median dorsal line of the Sauropsidan embryo there is a linear structure 
called the primitive streak divided into two parts by the neurenteric 
canal. Along the anterior part the hypoblast and epiblast are 
originally continuous; the posterior part belongs to the ventral 
surface of the body. The anterior part of the primitive streak 
represents the original blastopore, the posterior part, the coalescence 
of the non-inflected part of the edge of the blastoderm in Elasmo- 
branchs. The edge of the blastoderm in Sauropsida corresponds 
to a new ventral hernia apparently not continuous with the hernia 
in Elasmobranchs represented by the posterior part of the primitive 
streak. Thus no part of the edge of the blastoderm is homologous 
with the lip of the ancestral blastopore, or with the edge of the 
blastoderm in Teleosteans or Amphibia, or with the edge of the 
blastoderm in Elasmobranchs. 
The working out of these general views in detail will form 
an interesting subject for future researches in the comparative 
embryology of vertebrates. There is one point at present which is 
ripe for settlement, and that is, whether any part of the primitive 
blastopore extends in any vertebrate to the ventral side of the body. 
From the evidence of Teleostean development the answer to the 
question seems to be negative, but Sedgwick and Miss Johnson of 
Cambridge have brought forward some evidence that the posterior 
end of the blastopore in Triton gives rise to the permanent anus. 
Monday , 4 th May 1885. 
JOHN MURRAY, Esq., PhJD., Vice-President, 
in the Chair. 
At the request of the Council, an Address was given by R. T. 
Omond, Esq., on two years’ Residence and Work at the Ben Nevis 
Observatory. 
On the motion of the Chairman, a vote of thanks was accorded 
to Mr Omond for his Address. 
VOL. XIII. 
N 
