Hb 



LV PH 



NT 



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. ^, anus ; /-'j?, forebrain ; //i5, hindbrain ; Z. F, liver 

 diverticulum; A/i?, midbrain ; A'', notochord ; NT, neurenteric canal; 

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

 (From Morgan, after Marshall.) 



