138 DEVELOPMENT OF THE FROG'S EGG [Cii. 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 



Fig. OK — Sagittal sections through two stages: A. when blastopore is overarched ; 

 a. when amis has formed. (After Marshall, with modifications in A.) A. 4uus 

 Fb. Fore-brain. Hb. Hind-brain. LV. Liver-divertirulum. Mb. Mid-brain. 

 N. Notochord. NT. Xeurenteric canal. PD. Proctodffium. 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 



