DEVELOPMENT PRIOR TO LAYING 



33 



grating wall (Fig. 9). The chromosomes and nucleoli form a 

 group near the center of the upper plane surface of the germinal 



FIG. 9. Vertical section of the germinal vesicle and part of the germinal 

 disc of an ovarian ovum J inch in diameter; pigeon, x 385. (After 

 Harper.) 

 Chr., Chromosomes. Gr., Granulosa. G. V., Wall of germinal vesicle. 



vesicle. The first maturation spindle is formed before ovulation, 

 containing eight quadruple chromosomes (tetrads). The spindle 

 is still in the equatorial plate 

 stage when the ovum is 

 grasped by the mouth of the 

 oviduct (Fig. 10). The bulk 

 of the substance of the ger- 

 minal vesicle soon forms a 

 yolk-free cone extending 

 from the maturation spin- 

 dle deep into the superficial 

 yolk. The outer end of the FIG. 10. Vertical section of the germinal 



disc of the pigeon's egg showing the 



1 ______ 



Tetr. 





spindle is in almost imme- 

 diate contact with the sur- 

 face of the ovum. In the 

 later stages of formation of 

 the first polar body each 

 tetrad, or quadruple chromosome, separates into two dyads or 

 double chromosomes, and the members of each pair of dyads 

 separate and approach opposite ends of the spindle (anaphase). 



first maturation spindle. The egg was 

 clasped by the funnel of the oviduct. 

 8.50 P.M. x 2000. (After Harper.) 

 m. Sp. 1, First maturation spindle. Tetr., 

 Tetrad. 



