206 



NEURENTERIC CANAL. 



before the completion of the neural canal. The hind end of the alimentary 

 tract appears also to become a closed canal before this stage. 



In Lacerta muralis the history appears to be somewhat different, and 

 it is more especially to be noticed that in this species the hindgut does 

 not become closed till considerably after the completion of the neural 

 canal. In a stage shortly after that last described, the neurenteric passage 

 becomes narrower. The next stage which I have observed is considerably 



me 



FlG. 128. FOUR TRANSVERSE SECTIONS THROUGH THE HINDER END OF A YOUNG 

 EMBRYO OF LACERTA MURALIS. 



Sections A and B pass through the whole embryo, while C and D only pass 

 through the allantois, which at this stage projects backwards into the section of the 

 body cavity behind the primitive streak. 



ne. neurenteric canal ; pr. primitive streak ; kg. hind-gut ; hy. hypoblast ; //. body 

 cavity; am. amnion ; se. serous envelope (outer limb of the amnion fold not yet 

 separated from the inner limb or true amnion); al. allantois; me. mesoblastic wall of 

 the allantois; v. vessels passing to the allantois. 



later. The neural canal has become completely closed, and the flexure of 

 the embryo has already made its appearance. There is still a well-deve- 

 loped, though somewhat slit-like, neurenteric passage, but from the analogy 

 of birds, it is not impossible that it may have in the meantime closed up 



