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



37 



until they meet, and so form what is the ventral lip of the 

 now circular blastopore {^Fig. 21, A — D). In section it is 

 seen that there is a slight ingrowth at the lateral and at 

 the ventral lips of a plate of cells continuous with the 



Fig. 22. 



Hypogeophis (after Brauer). 



Three stages in the closure of the blastopore. 



A—C. Formation of the dorsal lip, archenteron, communication of the 

 latter with the segmentation cavity {s.c). formation of the yolk-plug and 

 ventral lip. Sagittal sections. 



D. Transverse section showing the lateral lips of the blastopore (/./.). 



similarly formed plate which forms the roof of the 

 archenteron in front ; beneath the plate is a slit-like 

 space, also, of course, archenteric ; in the midst of the 

 blastopore is the projecting typically Amphibian yolk- 



