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. PLATE LXVI. 



Fig. 1. — An early stage of the spermatocyte nucleus, succeeding syni- 

 zesis. (a;) Accessory chromosome, (p) Plasmasome. 



Figs. 2 and 3. — Same as fig. 1. 



Fig. 4. — Slightly later stage of the spermatocyte nucleus than is shown 

 in figs. 1, 2 and 3. The chromatin is more diffuse and the accessory 

 chromosome (x) is elongated, granular, and stains more deeply than the 

 other chromatin. 



Fig. 5. — A spermatocyte nucleus at the period of greatest diffusion. 

 The chromatin is reticular, (p) Plasmasome. (x) Accessory chromo- 

 some more condensed than the form shown in fig. 4. 



Fig. 6. — Same as fig. 5. The accessory is a homogeneous chromatin 

 rod and the plasmasome reaches its maximum size in this stage. 



Fig. 7. — Spermatocyte nucleus in early prophase, showing the first 

 signs of chromosome reorganization. (p) Vacuolated plasmasome. 

 (x) Accessory chromosome. The difference in the consistency of these 

 two bodies is apparent in iron-haematoxylin preparations which were 

 stained for a shorter time, comparatively, or which were subjected to a 

 longer extraction process. 



Fig. 8. — Spermatocyte nucleus, showing the beginnings of tetrad 

 formation and the accompanying phenomenon, the decrease in size of the 

 plasmasome. 



Fig. 9. — Later spermatocyte prophase. The plasmasome becomes 

 spherical as it disappears. 



Figs. 10 and 11. — Two parts of the same nucleus drawn from adjacent 

 sections. There are thirteen bodies, all of which are shown. The plas- 

 masome has diminished greatly in size, (m) The univalent halves of the 

 small chromosome. 



Figs. 12 and 13. — Spermatocyte cells in early prophase. The nuclear 

 wall in fig. 12 is not shown. The plasmasome is very lightly stained, in 

 marked contrast to the accessory, which holds the stain much longer. 



Fig. 14. — Accessory chromosomes drawn from spermatogonial cells in 

 metaphase. For the method of identification see text. 



Fig. 15. — Accessory chromosomes from cells of the same stage and 

 preparation as that of fig. 12, where there is no trouble in identifying 

 this element. 



Fig. 16. — Tetrads from the same stage and preparations as figs. 12 

 and 13. (a) Largest form. (6) and (c) Typical forms of the cross. 

 (d) The small chromosome, the halves of which are not usually so close 

 together at this time. 



Fig. 17. — Portion of a spermatocyte nucleus in late prophase, showing 

 the diminishing plasmasome (p) and the halves of the small chromo- 

 some (m). 



Figs. 18 and 19. — Portions of the same spermatocyte nucleus appear- 

 ing in adjacent sections, showing thirteen elements — nine tetrads, two 

 m-chromosome diads, the accessory chromosome, and the plasmasome. 

 The plasmasome has almost entirely disappeared. 

 Figs. 20 and 21.— Same as figs. 18 and 19. 

 Figs. 22 and 23.— Same as the two previous figures. 

 Figs. 24 and 25. — Same as above. The nuclear wall in fig. 25 is not 

 shown. 



