Manchester Memoirs, Vol. I. (1906), No. 3. 47 



dorsal lip, where they are perfectly continuous with the 

 sheets of mesoderm produced at the sides of and behind 

 the blastopore. The mesoderm thus exhibits all the re- 

 lations which it has in the Anamnia. 



The lining epithelium of the alimentary canal is 

 derived from the paraderm, which grows in from the sides 

 beneath the mesoderm and notochord towards the middle 

 line. The gut is subsequently folded off from this layer 

 in the ordinary fashion. 



The notochord and mesoderm may therefore be said 

 to be laid down in the Reptilia, as we have seen them to 

 be in the Anamnia, at the lips of and during the closure 

 of the blastopore, a closure moreover which is as bi- 

 laterally symmetrical here as it is there. 



We have only now to consider one or two interesting 

 points in some other forms. 



An embryonic shield distinct from the surrounding 

 blastoderm has been observed in most cases {Cistiido, 

 Emys, Trionyx, Lacerta, Tropidonotus, Crocodilus). 



A primitive plate is found in Lacerta and Tropido- 

 notus, but not in Emys. 



In Lacerta, according to Wenckebach, the lip of the 

 blastopore is not the only source of origin of notochord 

 and mesoderm ; both receive additions in front by the 

 proliferation of cells of the anterior paraderm. A similar 

 double origin of the middle layer has been described in 

 several other forms ; it^may be compared with the double 

 origin of the mesoderm in Petroniyzon, the Frog and some 

 other Anamnia. 



In Eviys on, the other hand the paraderm takes no 

 part in the formation of any portion of the embryo what- 

 ever, but gives rise to the lining of the yolk-sac alone. 

 The roof of the archenteron in this form splits into two 

 sheets, an upper, which again becomes sub-divided into 



