3TAGE "C" 

 >rm or the 



embryos is six hours older than "B'L has 

 been changed by the appearance of two lateral thick- 

 enings of the ectoderm a little posterior to the 

 median transverse- plane. Fig.G. 



The blastopore , which in "B"was open to the 

 exterior ,has closed leaving no trace of its former 

 position. 



The mouth arid oesophagus. which existed in "3" 

 only as a shallow ectodremal pit ,now have the form 

 of a deep hollow tube^ which projects vertically in- 

 ward until it passes through the hydrocoele and be- 

 yond the posterior enterocoele,when it curves back 

 under the latter to fuse withthe anterior wall of 

 the stomach . 



Wh-iis The stomach and posterior enterocoelo 

 are still in open communication .as in "B" .the fur- 

 row in "C" has deepened and the process by which 

 the two structures are being separated is almost 

 c ompl e te . Fig ,7 . 



Although the walls of the oesophagus and stomach 

 are fused, their cavities are sjill separate. 



This condition renders it easy to sec- what part 

 is played by the ectoderm in the formation of the 



