ii 



A 





4®^'"^""-=- v( ZONA PELLUCIDA 



-^ Sir'' 







YOLK 

 GLOBULES 





\<fit 



■'■'■\ 



H^ 





(tap ^^iffr- 



Fig. 125. Fertilization in the opossum. (A after McCrady, '38, from Duesberg; B-F 

 after Hartman, '16.) (A) Conjugate sperm of opossum. (B) Ovarian egg showing 

 discus proiigerus around the egg; first polar body extruded; chromosomes of egg nucleus 

 evident. (C) Tubal ovum. (D) Uterine ovum with pronuclei near center of the egg. 

 (E) First cleavage spindle of uterine egg. (F) Two-cell stage, showing zona pellucida 

 and exuded yolk material lying in perivitelline space. 



GERMINAL VESICLE 



FOLLICLE CELLS 

 VITELLINE 

 MEMBRANE 



CHROMATIN 

 P V SPACE 



*:■•■> -sJii' E. 



Fig. 126. Maturation and fertilization in the hen's egg. (Drawings from photomicro- 

 graphs by Olsen, '42.) (A) Cross section of germinal vesicle of almost mature egg, 

 showing the general position and condition of the intact germinal vesicle. (B) Egg just 

 prior to ovulation. Germinal vesicle spreading laterally as a thin layer below the ooplasmic 

 membrane. (C) Chromatin material near center of disintegrating germinal vesicle 

 (G.V.) of an egg estimated to be one hour prior to ovulation. (D) First polar body 

 (I P.B.) of recently ovulated egg. (E) Cross section of blastodisc of recently ovulated 

 egg showing male pronucleus ( i }, female pronucleus ( ? ), and second polar body 

 (2 P.B.). 



252 



