Fig. 3. — Egg of 

 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- 

 niiclRu.s. D. A view similar to the la.st. hut showinc onlv 



