40 THE FIRST PRINCIPLES OF HEREDITY 



number) ready for fertilization, and three polar bodies, 

 each with two chromosomes. The polar bodies, so far as 

 our present knowledge goes, seem to be functionless, and 

 'are lost. The accompanying illustration (Fig. 27) will 

 make the process still clearer. 



FIG. 29. SPERMATOGENESIS. (Adapted from O. Hertwig.) 



(From Weismann, " The Evolution Theory.") 



A , primitive sperm-cell with four chromosomes ; B, mother-sperm- 

 cell with eight chromosomes ; C, first maturation division ; 

 .D, formation of first two daughter-sperm-cells ; E, second 

 maturation division ; F, final four sperm-cells. 



The parthenogenetic ovum, as has now been abundantly 

 proved, divides only once for maturation that is, it first 

 doubles its number of chromosomes, and then extrudes 

 only one polar body, thus retaining the full original num- 

 ber of chromosomes. 



