MATURATION. 



25 



cells the single functional cell in the female as contrasted with four in the male 

 loses some of its character when one notes that in some forms the polar bodies 

 are not so rudimentary as is generally the case. Thus in certain forms one or 

 more of the polar bodies may develop into cells very similar to the mature egg- 

 cell, may be penetrated by spermatozoa, and may even be fertilized and proceed 

 a short distance in segmentation. There is perhaps warrant for considering 

 the polar bodies ar rudimentary or abortive ova. 



The time of formation of the polar bodies varies in different animals* In 

 a few (Echinoderms) they are formed before the sperm enters the egg. In 



Oogonia 



Primary 

 oocyte 



Secondary 

 oocyte 



Mature 

 ovum 



Prolifera- 

 tion 



Growth 



Maturation 



Trans- 

 formation 



FIG. 16. Diagrams representing the histogenesis of (a) the female sex cells and (6) the male sex 



cells. Modified from Boveri. 



Ascaris they are both formed after the entrance of the sperm. In other forms, 

 like the mouse, the first polar body is formed while the egg is still in the Graafian 

 follicle, the second one after the entrance of the sperm. 



From the data in the above description it is evident that the phenomena of 

 maturation are essentially similar in the male and female sex cells. In the 

 female two or three of the cells are indeed abortive, probably in order to insure 

 a large amount of food material to the functioning ovum; but the result, the 

 reduction of the number of chromosomes in the mature sex cell to one-half the 

 number characteristic of other cells of the species, is always the same. 



Significance of Mitosis and Maturation. 



The earlier investigators regarded maturation merely as a means of reducing 

 the number of chromosomes in the mature germ cells, so as to prevent a dou- 



