E H 



FIG. 24. Diagrams showing the essential facts in the maturation of the egg. 

 The somatic number of chromosomes is supposed to be four 



A, initial phase: two tetrads have -been formed in the germinal vescicle. , the two 

 tetrads have been drawn up about the spindle to form the equatorial plate of the first 

 polar mitotic figure. C, the mitotic figure has rotated into position, leaving the remains 

 of the germinal vesicle at g.v. D, formation of the first polar body : each tetrad 

 divides into two dyads. , first polar body formed: two dyads in it and also in the 

 e gg (A'*- 1 )- ^ preparation for the second division. G, second polar body forming and the 

 first dividing: each dyad divides into two single chromosomes. //, final result: three 

 polar bodies and the mature ovum, each containing two single chromosomes, or half 

 the somatic number ; c, the egg centrosome, which now degenerates and is lost. After 

 Wilson 



168 



