Outer cell. Outer cell* 



Zona 

 fcllucitla 



Outer celt- 



Outer cells. 



Inntr cells. 



Oute 



cell: 



Inner cells. 



FIG. 532. 1, 2, 3. DIAGRAMS ILLUSTRATING THE SEGMENTATION OF THE MAMMALIAN 

 OVUM (ALLEN THOMSON, AFTER VAN BENEDEN). 4. DIAGRAM ILLUSTRATING THE RELA- 

 TION OF THE PRIMARY LAYERS OF THE BLASTODERM, THE SEGMENTATION-CAVITY OF THIS 

 STAGE CORRESPONDING WITH THE ARCHENTERON OF AMPHIOXUS (BONNET). 



