6o 



REPRODUCTION AND LIFE HISTORY. 



the ovum was all-important, only needing the sperm's 

 awakening touch to begin unfolding the miniature model 



Fig. 27. — Spermatogenesis and polar bodies. — After 

 Hertwig and Weismann. 



A'. Primitive germ cell of Ascaris megalocephala., var. bivalens 



(4 chromosomes). 

 B'. Sperm mother cell (8 chromosomes). 

 C. Two spermatocytes formed, each with 4 chromosomes (first 



reducing division). 

 D'. Four spermatozoa formed, each with 2 chromosomes (second 



reducing division). 



A. Primitive germ cell (4 chromosomes). 



B. Fully developed ovum (8 chromosomes). 



C. Formation of first polar body (pb.i) (first reducing division). 



D. Formation of second polar body {j>b.z) (second reducing 



division). First polar body may divide into two. 



which it contained. Others, nicknamed "animalculists," 

 were equally confident that the sperm was essential, though 



