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internal 



a h 



Fig. 8. — Sections of successive stages showing the 

 phenomena of fertihzation in Nereis. 



a, Section of an egg 54 minutes after insemination. Cf. Fig. 3^. 

 The head of the spermatozoon has rotated, the sperm nucleus is becom- 

 ing rounded, and the sperm aster is beginning to arise opposite to the 

 cone. The latter marks the apex of the sperm head. The first polar 

 body is fully formed, h, The sperm cone-nucleus-aster complex of an 

 egg 64 minutes after insemination. The sperm cone is now separated 

 from the nucleus, and is destined soon to disappear. The sperm aster 

 and centrosome better developed. 



Fig. 8 (continued). — c, 67 minutes after insemination; stage of 

 anaphase of second maturation division. The sperm aster has divided, 

 forming an amphiaster. d, jy minutes after insemination. The sperm 

 nucleus Hes to the left below; the sperm amphiaster has become reduced. 

 The egg nucleus, which is formed by fusion of chromosome vesicles, 

 is represented by two still unfused parts to the right above. 



