nk 1 



cspkf^ 



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 andRki) ; C, sperm-nucleus ( S k) and ovum-nucleus 

 C^ 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. 



