124 



THE DEVELOPMENT OF THE GAMETES OR SEX CELLS 



Species 



Place of Origin, etc. 



Author 



Felis domestica Definitive ova derived from germinal Kingsbury. 1938. 



(cat) epithelium of the ovary at an early Am. J. Anat. 15 



stage of gonad development 



Cavia porcellus Primordial germ cells from entoder- 



(guinea pig) mal origin degenerate; the primor- 



dial germ cells derived from the 

 germinal epithelium give rise to 

 the definitive germ cells in the 

 testis 



Bookkout. 1937. 

 Zeit. f. Zellforsch, 

 mikr. Anat. 25 



Homo sapiens Primordial germ cells found in en- 



(man) toderm of yolk sac; migrate by 



ameboid movement into develop- 

 ing gonad 



Witschi. 1948. 



Carnegie Inst., Wash- 

 ington Publ. 575. 

 Contrib. to Embryol; 

 32 



C. Maturation (Differentiation) of the Gametes 



1. General Considerations 



Regardless of their exact origin definitive germ cells as primitive oogonia 

 or very young oocytes are to be found in or near the germinal epithelium 

 in the ovaries of all vertebrates in the functional condition (figs. 39B, 64). 

 In the testis, the primitive spermatogonia are located within the seminiferous 

 tubules as the germinal epithelium, in intimate association with the basement 

 membrane of the tubule (figs. 65, 66). 



The period of coming into maturity (maturation) of the gametes is a com- 

 plicated affair. It involves profound transformations of the cytoplasm, as 

 well as the nucleus. Moreover, a process of ripening or physiological ma- 

 turing is necessary, as well as a morphological transformation. The phrase 

 "maturation of the germ cells" has been used extensively to denote nuclear 

 changes. However, as the entire gamete undergoes morphological and physio- 

 logical change, the terms nuclear maturation, cytosomal maturation, and 

 physiological maturation are used in the following pages to designate the 

 various aspects of gametic development. 



One of the most characteristic changes which the germ cell experiences 

 during its maturation into a mature gamete is a reduction of chromatin ma- 

 terial. Because of this, the germ cell which begins the maturing process is 

 called a meiocyte. This word literally means a cell undergoing diminution and 

 it is applied to the germ cell during meiosis or the period in which a reduction 

 in the number of chromosomes occurs. The word haplosis is a technical 

 name designating this reduction process. 



The word meiocyte thus is a general term applicable to both the developing 



