MATURATION OF THE GERM-CELLS 



47 



i there is a parallel reduction in the number of chromosomes to 

 II one-half. 



A B 



P.G.C. « 

 OG ( 



OC 



A l\ 



* » • • 



A A A. !Y~. 



•w 



P.G.r. • 



5G* 



,U 



SC 



• • c • 



// /I /\ l\ 



O.r 



Ob 



Oc 





Sa 



Sb- 

 Sc. 



:/\ /\„.J 



P.L' 



Fig. io. — Parallelism of oogenesis (A) and spermatogenesis (after Boveri). 



P.G.C. in both series (A and B), one of the primitive germ cells. 



Following the oogenesis (A), there is first of all a period of multiplication (M), included 

 within the first bracket. 



The primitive germ-cell gives rise to oogonia {OG). 



These oogonia give rise to oocytes (OC). 



Then follows a period of growth (G), included within the second bracket. 



Then follows the process of ripening or maturation (R), included within the third bracket. 



Od, the immature ovum, with the normal number of chromosomes. 



P.B', the first polar body, usually separated off by a meiotic or reducing division which 

 lessens the number of chromosomes to one half the normal. 



Ob, the ovum after giving off the first polar body, with half the normal number of chromo- 

 somes. 



P.B", the second polar body, formed by an ordinary equation division. 



Oc, the ripe ovum. 



P.h', the first polar body has divided into two by an equation division. 



Following the Fpermatogenesis (B), there are successive periods (or zones in the testis) 

 of multiplication (M) , growth (G), and reduction (K). 



The primitive germ-cell gives rise to spermatogonia (SG). 



These spermatogonia give rise to spermatocytes (SC). 



Immature spermatocytes of the first order [Sa) have the normal number of chromosomes. 

 In many cases by a reduction or meiotic division they give rise to spermatocytes of the 

 second order (Sb), with half the normal number of chromosomes. 



These give rise by an eq nation division to spermatozoa [Sc). 



'The one fact of maturation that stands out with perfect 

 clearness and certainty amid all the controversies surrounding it 

 is a reduction of the number of chromosomes in the ultimate germ- 

 cells to one-half the number characteristic of the somatic cells. It 

 is equally clear that this reduction is a preparation of the germ- 



