Outer cell. 



Outer cells. 



Polar bodies 



Inner cell 



Inner celh 



Inner cells. 



Outer cells. 



Inner cells 



Inner cells. 



Outer cells. 



FIG. 16. Diagrams showing the segmentation of the mammalian ovum and the formation of the blasto- 

 dermic vesicle (Allan Thomson, after van Beneden). 



