138 



DEVELOPMENT OF THE FROG'S EGG [Cn. XIII 



meet above and posterior to the blastopore, so that the latter 

 can no longer be seen from the surface (Figs. 23, D, E, and 

 37, A). As a result the central canal of the nervous system 



H B 



PH 



FIG. 37. Sagittal sections through two stages : A. when blastopore is overarched ; 

 B. when anus has formed. (After Marshall, with modifications in A.) A. Anus. 

 FB. Fore-brain. HB. Hind-brain. LV. Liver-diverticulum. MB. Mid-brain. 

 N. Notochord. NT. Neurenteric canal. PD. Proctodseum. PH. Pharynx. 

 PN. Pineal body. PT. Pituitary body. 



becomes continuous at its posterior end with the overarched 

 blastopore, and by means of the latter the so-called neurenteric 



