Fig. 130. Fertilization in Nereis. (After F. R. Lillie, '12.) (A) Sperm of Nereis, 

 entire. (B) Egg of Nereis, 15 minutes after insemination. The fertilization cone is evi- 

 dent below point of sperm contact. Observe that the intact germinal vesicle is present 

 in the center of the egg. It will break down as the sperm enters the egg (G). The cortical 

 substance from the empty cortical compartments in the cortical layer shown around the 

 periphery of the egg has passed out through the vitelline membrane to form the jelly 

 layer around the egg. (C~G) Entrance of the sperm head into the ooplasm of the egg 

 as the fertilization cone substance is withdrawn inward from the vitelline membrane. 

 (C) Fifteen minutes after insemination. (D) Thirty-seven minutes after insemination. 

 (E) Forty-eight and one-half minutes after insemination. (F) Fifty-four minutes after 

 insemination. (G) Sperm head has completed penetration. Observe that the middle 

 piece of the sperm remains outside, attached to the vitelline membrane. Anaphase of 

 first maturation division. 



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