MATURATION OF THE OVUM THE FEMALE GERM CELL 



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process consists in the development of a tail or cilium, the transformation of 

 the nucleus into the form of a spermatozoon head, and the sloughing off 

 of nearly all the remaining cell protoplasm. The centrosome, a minute body 

 closely concerned with the power of cell division, is apparently retained, but 

 the power of cell division is impossible in the presence of so little cytoplasm, 

 figure 499. 



FIG. 501. The Maturation of the Ovum; Extrusion of the "Polar Bodies." (Dia- 

 grammatic.) A, An ovum at the commencement of the process; B, after the formation of 

 the spindle. The chromosomes are gathered at the equator of the spindle. C, One apex 

 of the spindle has projected into a bud on the surface, and half of the divided dyads have 

 passed to each pole; D, the separation of the first polar body; E, the commencement of the 

 second polar body; F, the completion of the second polar body. (Cunningham.) 



Maturation of the Ovum the Female Germ Cell. The ovum when 

 liberated from the ovary is a single cell enclosed within the zona pellucida, 

 and containing the germinal vesicle or nucleus and germinal spot or nucleolus. 

 It still possesses the somatic or double number of chromosomes, and must 

 undergo maturation divisions in order to reduce their numbers. Previous 

 to the maturation divisions it should more correctly be called a primary 

 oocyte. 



Synapsis now occurs in the nucleus. It is not fundamentally different 

 from the synapsis in the spermatocyte. Meanwhile the nucleus migrates 

 to the surface of the oocyte. After synapsis, the chromosomes are in the form 

 of a single set of tetrads as in the male. They are liberated by the disappear- 



