E 



FIG. 155. Series of diagrammatic drawings of sections showing the process 

 of gastrulation in the Urodele, Triton. After Greil and Ruffini. F. Transverse 

 section, others sagittal. A. Blastula. B. Commencement of gastrulation 

 (invagination). C. Continued invagination accompanied by epiboly and invo- 

 lution. Formation of archenteron. D. Continuation of all three processes 

 of gastrulation. Blastocoel nearly obliterated. E. Archenteron completely 

 formed. Rudiments of notochord and neural plate differentiated. F. Trans- 

 verse section through embryo shown in E, through the plane marked ff. a, 

 archenteron (gut cavity in F) lined with endoderm; b, blastopore; ch, rudiment 

 of notochord; ec, ectoderm; en, qpdoderm; ff, plane of section shown in F; gm, 

 gastral (axial) mesoderm ; n, neural plate (in F, bounded by neural folds) ; pm, 

 peristomial mesoderm; s, blastocoel or segmentation cavity; x, marks corre- 

 sponding points on the surface ectoderm, showing extent of epiboly; y, yolk cells. 



