THE FEMALE 



65 



egg, surrounding the chromosome frame. This frame is a gel struc- 

 ture which gives rise to the first maturation spindle, containing 13 

 pairs of slightly contracted chromosomes. 



These structural features can be observed in the living germinal 

 vesicle if it is removed from the oocyte and placed in isotonic and 

 balanced salt medium, omitting the calcium ion. A minute amount of 

 NaHoPO, is added to shift the pH toward the acid side, which makes 

 the chromosomes the more visible. Or, the chromosomes may be 



Colloid ground 

 substance 



Central 

 chromosome core 



Nuclear 

 membrane 



Isolated germinal vesicle (nucleus) of Rami pipiens. Nucleus isolated in 

 calcium-free Ringer's solution, from stage 6, showing sac-like organelles which 

 protrude from the nuclear membrane. The cloud of central nucleoli surrounds 

 and obscures the chromosome frame. (Courtesy, W. R. Duryee, 1950, Ann. 

 N. Y. Acad. Sci., 50, Art. 8.) 



