GASTEULATION 



43 



between the two cavities so that they form a continuous space — the 

 broader front part of which is derived from the segmentation cavity, 

 the narrower posterior part from the true archenteron (Fig. 27, C 



M*$&* 



B 



'■•• *'■' ■ ilfllfli 







Fig. 27. — Sagittal sections illustratiug the process of gastrulation in Hypogeophis. 

 (After Brauer, 1897.) 



ect, ectoderm ; ent, archenteric cavity ; f/.l, gastrular lip ; s.c, segmentation cavity. 



and D). The two sections of the cavity remain for a time clear In- 

 distinguishable by the character of the cells which form the roof 

 — those of the archenteric portion being composed of fine-grained 

 protoplasm like that of the ectoderm while those of the portion 

 derived from the segmentation cavity are typical yolk-cells. 



