120 



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-O, successive stages in 

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

 chromosomes in each germ nucleus; I, first cleavage spindle 

 showing chromosomes from egg and sperm on opposite sides 

 of spindle. (After Sobotta.) 



