38 



EMBRYOLOGY 



4. Telophase. The cell protoplasm begins to appear constricted around the 

 equator of the achromatic spindle, where double rows of granules are also sometimes 

 seen. The constriction deepens and the original cell gradually becomes divided 

 into two new cells, each with its own nucleus and centrosome, which assume the 

 ordinary positions occupied by such structures in the resting stage. The nuclear 

 membrane and nucleolus are also differentiated during this phase. 



I 



VI 



FIG. 2. Diagram showing the changes which occur in the centrosomes and nucleus of a cell in the process of mitotic 

 division. (Schafer.) / to ///, prophase; IV, metaphase; V and VI, anaphase; VII and VIII, telophase. 



THE OVUM. 



The ova are developed from the primitive germ cells which are imbedded in 

 the substance of the ovaries. Each primitive germ cell gives rise, by repeated 

 divisions, to a number of smaller cells termed oogonia, from which the ova or 

 primary oocytes are developed. 



Human ova are extremely minute, measuring about 0.2 mm. in diameter, and 

 are enclosed within the egg follicles of the ovaries; as a rule each follicle contains 



