FIG. 12. Maturation of the egg of Cyclops (the full number of chromo- 

 somes is not shown) : A, germinal vesicle with the chromosomes 

 already split longitudinally. B, the chromatin masses shortened, 

 with indication of transverse division to form the tetrads. C, the 

 young tetrads arranging themselves on the first polar-body spindle. 

 D, tetrads in first polar-body spindle. E, separation of the dyads 

 in the same. F, position of the dyads in second polar-body spindle ; 

 the first polar body is shown above the margin of the egg. (After 

 Ruckert.) 

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