102 OUTLINES OF CHORDATE DEVELOPMENT 





E 



F 



FIG. 33. Frontal and transverse sections through gastrulas of the frog 

 (R. temporaria) of various ages. After Brachet. A. Frontal section through 

 gastrula of same age as Fig. 32, C. B. Frontal section through gastrula of 

 same age as Fig. 32, D. C. Frontal section through gastrula slightly older than 

 Fig. 32, F. D. Frontal section through gastrula of same age as Fig. 32, G. 

 E. Transverse section through gastrula slightly older than Fig. 32, D. F. Trans- 

 verse section through gastrula slightly older than Fig. 32, G. a, Archenteron; 

 6, blastopore; c, notochord; ge, gut endoderm; m, peristomial mesoderm; np, 

 neural plate; s, segmentation cavity or blastoccel. 



