THE CONTINUITY OF LIFE 



247 



Nucleolus 



Nuclear membrane 



Cytoplasm. 



Oil droplet 



A 

 Chromosomes 



Fig. 166. — Maturation and fertilization of the egg of the Sandworm, 

 Nereis. A, egg (oocyte) before start of maturation; B, first polocyte spindle 

 forming, sperm just entering; C, first polocyte spindle established; D, first 

 polocyte formed, second polocyte spindle near; spindle with sperm nucleus; 

 E, second polocyte formed, union of egg and sperm nucleus; F, spindle for 

 first division of fertilized egg. Note that in Nereis, as in many other animals, 

 maturation of the egg is deferred until the time of fertilization. (From Wilson.) 



