FIG. 3. Egg of a 

 mouse previous to 

 maturation. (After 

 Kirkham.) 



FIG. 4. Maturation and fertilization of the egg of a mouse. 

 A. The first maturation division in progress. B, The first 

 polar-cell fully formed ; the second maturation division 

 in progress. C. The second maturation division com- 

 pleted ; the second polar-cell is the smaller one ; near it, 

 in the egg, is the egg-nucleus, and at the left is the sperm- 

 nucleus. D. A view similar to the last, but showing only 

 one polar-cell, the second; note its twelve distinct 

 chromosomes ; near the sperm-nucleus in the egg, at 

 the left, is seen the thread-like remains of the sperm-tail. 

 (After Kirkham.) 



