1^ 



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PLATE LXVIII. 



Figs. 1 to 10, inclusive. — The chromosome complex of the first sperma- 

 tocyte in metaphase. (x) Accessory chromosome. 



Fig. 5.— An unusual condition of the first spermatocyte metaphase, 

 showing twelve elements, a-a. — Probably the disjoined halves of one of 

 the larger chromosomes which normally occurs in the ring. 



Fig. 11. — Drawings of the accessory chromosome from cells of the 

 cyst from which fig. 6 was made, showing the constancy in size in this 

 element within a single cyst. 



Fig. 12. — Drawings of the accessory chromosome from cells of the 

 cyst from which fig. 7 was made. 



Fig. 13. — Drawings of the accessory chromosome from cells of the 

 cyst from which fig. 8 was made. 



Fig. 14. — Drawings of the accessory chromosome from cells of the 

 cyst from which fig. 9 was made. 



Fig. 15. — Drawings of the accessory chromosome from cells of the 

 cyst from which fig. 10 was made. 



Fig. 16. — Lateral view of first spermatocyte in beginning anaphase. 

 (x) Accessory chromosome. The cell membrane is shown. 



Fig. 17. — First spermatocyte spindle, in longitudinal section through 

 the accessory chromosome (a;), (a) and (6) Chromosomes of the ring 

 at equal distances from (m) , the central small chromosome. The acces- 

 sory chromosome lies outside of the ring, causing the asymmetry of the 

 spindle, as drawn. 



Fig. 18. — Same view of a slightly later stage, showing the typical 

 irregularity in the movements of the accessory chromosome (x) and the 

 central small chromosome (m) with respect to those of the ring (a) 

 and (6). 



Fig. 19. — Later anaphase, showing the difference in organization be- 

 tween the accessory chromosome (x) and the ordinary chromosomes. 



Figs. 20, 21 and 22. — Later successive stages of the first spermatocyte 

 anaphase, (x) Accessory chromosome. 



Figs. 23, 25 and 26. — First spermatocyte telophases, in which the acces- 

 sory chromosome (x) may still plainly be identified. 



Fig. 24. — Telophase of first spermatocyte. (x) Unusual element, 

 which is probably an undivided accessory chromosome or a persistent 

 plasmasome. 



