DEVELOPMENT PRIOR TO LAYING 



33 



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

 rr^iir* noar the center of the upper plane surface of the germinal 



group ne 



''0 M> '•^- ^-^ _^'^^' >' 





. r^ 



'W-'i^-^-^S:: 





• -^ ' ' • ' ' ''/:'' '1 ■ ' ■ ' '•' — -••' 



'xS^ 



•V/^ ' 



^^c 



~Q- 



^ ^y 



-Q^ 



Fig. 9. — Vertical section of the germinal vesicle and part of the germinal 

 disc of an ovarian ovum | 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 p. ■.-,-._■•_ — -=— 

 stage when the ovum is f ^ '15 

 grasped by the mouth of the i '/// 



oviduct (Fig. 10). The bulk | V^ 



of the substance of the ger- o 



minal vesicle soon forms a ' V^ ^>^--' 



yolk-free cone extending 

 from the maturation spin- 

 dle deep into the superficial L 

 yolk. The outer end of the 

 spindle is in almost imme- 

 diate contact with the sur- 

 face of the ovum. In the 

 later stages of formation of 





a: Q . . 



© 



llr 



^ 



-Tetr. 



Fig. 10. — Vertical section of the germinal 

 disc of the pigeon's egg showing the 

 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., 

 the first polar body each Tetrad. 



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). 



