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H. E. Jordan 
Fig. 10. Metaphase of the first maturation mitosis. This is the stage at- 
tained by the ovarian egg just prior to spawning and fertilization. The centro- 
some is large, spherical and very chromatic. It is surrounded by a homogeneous 
centrosphere bounded by a granulär layer ("microsome circle”) in which the 
astral rays appear to end. The nucleolus persists as an irregulär pale-staining 
mass with a ragged chromatic shell. The chromosomes are large, very chro- 
matic and mostly of variously modified cross-shapes (tetrads . The bivalent 
chromosomes appearing as paired rods bare not yet become definitely orieuted 
with respect to the spindle fibers. Their final position will be transverse to 
the fibers, and, becoiuing medially or sub-medially attached to the latter, will 
be drawn toward the opposite poles giving rise to typical cross-forms. 
Fig. 11. Median longitudinal section of similar stage showing a portion 
of all of the 18 bivalent (reduced n ^".ber) chromosomes. 
Plate XVII. 
Fig. 12. Metaphase spindle of ovarian egg showing chromosomes at several 
stages of division and the centrosome in process of fragmentation. 
Fig. 13. Equatorial plates of chromosomes of first maturation spindle. The 
reduced number of chromosomes is 18. 
Fig. 14. Stage immedietcly after spawning and fertilization. Most of the 
chromosomes are at early anaphase of the first (eqnation?) division. A few of 
the chromosomes are still at prophase. The single chromatic centrosomes have 
disappeared, and the centrosphere has become finely granulär. 
Fig. 15. Late anaphase of first maturation mitosis. Chromosomes appear 
as paired rods or loops representing probably transversely split univalent chro- 
mosomes. , 
Fig. 16. Egg at telophase of first mitosis. Three spermatozoa at different 
stages of metamorphosls into male pronuclei are shown. 
Fig. 17. a) Polar view of chromosomes at anaphase of first maturation 
division. bl Of second maturation division. Number of chromosomes is 18. 
Figs. 18, 19, 20 & 21. Stages iu the formation of the first polar body and 
the second maturation spindle; no centrosomes can be demonstrated. 
Fig. 22. Stage in the rotation of the second spindle from tangential to 
radial position. Chromosomes of first polar body are fusing. Later stage in 
formation of male pronucleus also shown. The polar body is flattened and rests 
in a concavity on the surface of the egg. 
Plate XVin. 
Figs. 23, 24 & 25. Successive stages in the formation of the second polar 
body. The chromosomes, resulting from a Segmentation of the V-or U-shaped 
chromosomes of the anaphase of the first mitosis at the apex, are simply drawn 
apart during the second maturation mitosis. 
Fig. 26. Mature ovum showing both polar bodies and early phase in for- 
mation of female pronucleus from a mass of small vesicles. Subsequently, the 
latter coalesce to form two larger vesicles (Fig. 27) which ultimately unite to 
form the definitive pronucleus. All indications of asters have disappeared. 
Figs. 27, 28 & 29. Stages iu the formation of the first cleavage spindle. 
The asters lack a centrosome and the pronuclei a nucleolus. 
