A L 



Fig. 12. A. — Sagittal section of embryo shown in Fig. ii, 



D, SHORTLY BEFORE THE CLOSURE OF THE BLASTOPORE. (After 



Marshall.) 



B^ blastopore. BF, fore-brain. B/f, hind-brain, BM, mid-brain. //, 

 entoblast. i, liver. M^ mesoblast. MN, mesenteron. 7V^, notochord. A^C, 

 neurenteric canal. /*, beginning of pituitary body as in growth of ectoblast. 

 PZ?, proctodaeum. R^ rectal diverticulum of mesenteron. S, central canal of 

 spinal cord. K, yolk-cells. 



B. — Sagittal section of embryo shown in Fig. i r , E , shortly 

 AFTER the closure OF THE BLASTOPORE. (After Marshall.) 



BF, fore-brain. B H, hind-brain. B M, mid-brain. CN^ notochord. M, 

 mesoblast. iVC, neural tube. A^ 7", neurenteric canaL PA'", pineal body. PT^ 

 pituitary body. T/, intestinal region of mesenteron. TP, pharyngeal region of 

 mesenteron. i/, proctodseal or cloacal opening. PF, liver. >', yolk-cehs. 



33 



