Manchester Memoirs, Vol. l. {igo6), No. ^. 53 



We can now summarize the principal facts for the 

 Amniota as follows : 



(i) A bilateral blastopore is formed within the 

 blastoderm and towards its posterior end. 



(2) The blastopore leads into an archenteron, which 



is also bilateral, its extent being greatest beneath 

 the dorsal lip. The archenteron is developed 

 wholly from the upper layer. 



The primitive groove of Birds and Mammals 

 is a laterally compressed blastopore, the ' neuren- 

 teric canal ' (' chorda - canal '), a rudimentary 

 archenteron. 



(3) The floor of the archenteron fuses with the para- 



derm secondarily, its cavity secondarily with 

 the subgerminal cavity. The roof of the archen- 

 teron is then inserted by its edges into the 

 outlying paraderm. 



(4) The notochord is formed from the roof of the 



archenteron in front of the dorsal lip, the meso- 

 derm from the same layer at the lateral lips, the 

 two sheets of mesoderm being continuous behind 

 the blastopore. Additions may be made to the 

 notochord and mesoderm from the paraderm. 



(5) The lining of the alimentary canal is usually, 



though not always, a derivative of the paraderm. 



(6) As in the Anamnia, discrepancies are observable 



in the destinies of sets of cells of similar origin. 



It only remains for us to consider the possibility of 

 deriving the Amniote from the Anamnian condition. 



