62 



REPRODUCTION AND LIVE HISTORY. 



The extrusion of polar globules and the associated reduc- 

 tion is almost universal in the history of ova, but in most 



A' 



B 



B 



FIG. 30. Spermatogenesis and polar bodies. After 

 Hertvvig and Weismann. 



A'. Primitive germ cell of Ascaris incgalocepJitTla, var. bhalcns 



(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 (/>/>. i) (first reducing division). 



1). Formation of second polar body (p/>. 2) (second reducing; 

 division). First polar body may divide into two. 



parthenogenetic ova only one polar body is formed, and 

 there is no reduction in the number of chromosomes. 



