DEVELOPMENT OF THE FROG S EGG. 



303 



The broken lines shown in Fig. 4 bear numerals which corre- 

 spond to the planes of section represented by the succeeding 

 figures, 7 and 8. The cross-section represented by 7, therefore, 

 passes through the embryo at the level of the fold in the neural 

 tube. The two halves of the yolk mass with sections of the 



FIG. 7. 



enteron which belong, the one to the cephalic end and the other 

 to the caudal end of the embryo, are shown separated from each 

 other by a deep cleft lined by ectoderm. Dorsal to the enteron 

 lie two sections of the notochord with the myomeres sectioned 

 in their long-axis between them. Between and dorsal to these 



FIG. 8. 



two portions of the notochord, the oblique section of the bend 

 in the neural tube, demonstrating the neurocele as well, is to be 

 seen. The level represented by Fig. 8 includes the region of the 

 brain and subjacent pharynx to the right and the trunk to the 



