THE OVUM. 



451 



filled with irregular columns or rods of epithelial cells, arranged 

 for the most part vertical to the surface. 



The primitive ova. The columnar epithelial cells of the 

 surface layer are at first all much the same size, but they do not 

 long remain so. At an early period, about the sixth or seventh 

 week, certain of the cells become conspicuous by their larger 

 size and more spherical shape ; these are the primitive ova 

 (Fig. 171, c, c), each of which is capable of developing into a 

 definitive or permanent ovum, and then, if fertilised, of giving 



Fig. 171. 



-Part of a vertical section of the ovary of a new-born Infant. 

 (From Strieker's ' Histology.') x 150. 



a, superficial layer of columnar epithelium, b, plate of epithelial cells, formed by 

 irregular growth of the ovary, c c, primitive ova. de, nests of various shapes, containing 

 ova and commencing follicles. /, isolated follicle with its contained ovum, g, blood- 

 vessel. 



rise to an embryo. Each of these enlarged epithelial cells is in 

 fact a potential human being. 



On the formation of the egg columns, by proliferation of the 

 deeper surface of the germinal epithelium, the primitive ova are 

 carried down into them in large numbers. As the egg columns 

 penetrate deeper and deeper into the substance of the ovary, 

 they become broken up, by further growth of the connective 

 tissue, into groups or nests of cells (Fig. 171, d, e), each nest 

 containing one or more primitive ova as well as a number of 

 indifferent epithelial cells. In these nests a tendency soon 



G o 2 



