THE MECHANISM OF HEREDITY 33 



The Mechanism of Mendel's Two Laws. 



Toward the end of the ripening period of the germ- 

 cells, chromosomes of the same size come together in 

 pairs. This is followed by a division of the cell, when the 

 members of each pair go into opposite cells. Each mature 

 germ-cell comes to contain only one set of chromosomes, 

 (Figs. 21 and 22). 



Fig. 21. 

 Diagram of the two maturation divisions of sperm-cells. Three 

 pairs of chromosomes are represented; those from the father in 

 black, those from the mother in white (except in a, b, c). The 

 first maturation division, here the reduction division, is shown in 

 d, e, f. The second, or equational division, in which each chromo- 

 some splits lengthwise into two daughter chromosomes, is shown 

 in g, h. 



