16 



HEREDITY AND ENVIRONMENT 





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Fig. 3. Entrance of the Spermatozoon into the egg or 

 the Annelid Nereis. A, Entire Spermatozoon, showing per- 

 foratorium (P) ; head (H) ; middle-piece (M), and tail (T). 

 B-G, Successive Stages in the Maturation and Fertilization 

 showing the progress of the entrance cone (EC) and sperm 

 nucleus (£N) into the egg. D shows the first maturation 

 spindle of the egg (1st Mat. Sp.) ; E the first polar body 



