76 THE FIRST PRINCIPLES OF HEREDITY 



as grandmother (first generation) will have 16 Idants each, 

 which number is reduced in their germ-cells to half i.e., 

 to 8 ; 8 Idants of the grandfather (denoted black) unite 

 with 8 Idants of the grandmother (denoted white) to form 

 the parent (second generation). The germ-cells of this 

 parent will, again, contain only half the number of Idants 

 i.e., again 8 Idants. But now the division may separate 

 the Idants in any combination of black and white Idants ; 

 for the line of division may fall in any direction, as indicated 



I Gen 



HGen 



FIG. 41. CONTRIBUTIONS OF ANCESTORS. (After Weismann.) 



by the arrow in the figure of the parental germ-plasm 

 (second generation) . Thus we may get in the third genera- 

 tion 8 black or 8 white Idants only, or a combination of 

 7 black and I white, 6 black and 2 white, etc., or any other 

 possible combination of black and white Idants, making 

 together 8 Idants. (These, in conjunction with 8 Idants 

 the shaded parts derived from another ancestral line give 

 again 16 Idants as the germ-plasm of the grandchild.) 

 A grandparent may therefore be represented in the grand- 

 child by any number of Idants from 8 downwards to o 



