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HEREDITY AND ENVIRONMENT 



FIG. 25. MATURATION AND FERTILIZATION OF THE EGG OF 

 THE MOUSE. A, first polar body and second maturation spin- 

 dle; B, second polar body and maturation spindle; C, entrance 

 of the spermatozoon into the egg; D-G, successive stages in 

 the approach of egg and sperm nuclei; //, formation of 

 chromosomes in each germ nucleus; /, first cleavage spindle 

 showing chromosomes from egg and sperm on opposite sides 

 of spindle. (After Sobotta.) 



