GENERAL OUTLINE 



177 



To Biitschli ('76,) Hertwig, and Giard ('77) we owe the discovery 

 that the formation of the polar bodies is through mitotic division, the 

 chromosomes of the equatorial plate being derived from the chro- 



D 



E H 



Fig. 88. Diagrams showing the essential facts in the maturation of the egg. The somatic 

 number of chromosomes is supposed to be four. 



-/. Initial phase; two tetrads have been formed in the germinal vesicle. B. 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. 

 E. First polar body formed ; two dyads in it and in the egg. F. Preparation for the second 

 division. G. Second polar body forming and the first dividing; each dyad divides into two 

 single chromosomes. H, Final result; three polar bodies and the egg-nucleus ($), each con- 

 taining two single chromosomes (half the somatic number) ; c, the egg-centrosome which now 

 degenerates and is lost. 

 N 



