FIG. 31. FERTILIZATION IN ASCARIS MEGALOCEPHALA. (Adapted 

 from Boveri and Van Beneden.) 



(From Weismann, " The Evolution Theory."} 



A , spermatozoon (sp) about to penetrate ovum which has one polar 

 body (Rki); B, spermatozoon (spk) with its centrosome (csph) has 

 entered ovum, which shows ovum-nucleus (Eik) and three polar 

 bodies (Rki andRk2) ; C, sperm-nucleus ( $ k} and ovum-nucleus 

 ( ? k} show each two chromosomes ; D, coalescence of sperm- 

 and ovum-nucleus into segmentation nucleus ; E, division of 

 segmentation nucleus ; F, formation of the first two embryonic 

 daughter-cells. 



