H B 



MB 



B 



FIG. 25. Sagittal sections through two embryos. In A the blastopore is 

 overarched and there is the beginning of the proctodaeum or anal invagi- 

 nation. In B the proctodaeum has met and fused with an evagination of 

 the archenteron. A, anus ; FD, forebrain ; HB, hindbrain ; L V, liver 

 diverticulum ; MB, midbrain ; N, notochord ; NT, neurenteric canal; 

 PD, proctodreum ; PH, pharynx; PN, pineal body; PT, pituitary body. 

 (From Morgan, pfter Marshall.) 



105 



