114 



HEREDITY AND ENVIRONMENT 



Fig. 25. Maturation and Fertilization of the Ego of 

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

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

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

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

 chromosomes in each germ nucleus ; /, first cleavage spindle 

 showing chromosomes from egg and sperm on opposite sides 

 of spindle. (After Sobotta.) 



