Fig. 127. Maturation and fertilization in Echidna. (Courtesy, Flynn and Hill, '39.) 

 (A) Oocyte, diameter 3.9 by 3.6 mm. Section. of upper pole of egg showing saucer-shaped 

 germinal vesicle lying in the germinal disc. (B) First polar spindle of egg just previous 

 to ovulation. (C) First polar body and chromatin of female nucleus just previous to 

 formation of second polar spindle shown in (D). (D) Second polar spindle of newly 

 ovulated egg. Sperm presumably enters germinal disc at this time but possibly may wait 

 until condition shown in (E) in some instances. (E) Second polar body and female 

 pronucleus. (F) Male and female pronuclei. (G, H) Fusion stages of pronuclei. 



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