158 KANSAS UNIVERSITY QUARTERLY. 



Fig. 7. Fragment of cell (shown also in fig. D), having chromatin threads split 

 longitudinally. 



Fig. 8. Late prophase — just before division. 



Figs. 9 and 10. Oblique sections of primary spermatogonia in metaphase. 



Fui. 11. Telophase of primary spermatogonium. 



Fiu. 12. Cross-section of "fingers" of nucleus of later telophase. 



Fig. 13. Cell at dividing line between metaphase of one cycle and prophase of 

 the next. Accessory chromosome shown as small dense body on the right. 

 As in fig. 12, the section is through the "fingers" of the nucleus. 



Fig. 14. Lateral view of early prophase of secondary spermatogonium, showing 

 characteristic form and arrangement of young spiremes. 



Fig. 15. Fragment of secondary spermatogonium in later prophase, showing 

 the "hand of the glove" containing the ends of all the spiremes. The irreg- 

 ular body at the right is a portion of the accessory chromosome — the rest 

 being cut away. At A is a complete accessory chromosome with its mem- 

 brane, drawn from another cell of the same cyst. Below may be seen a per- 

 sisting spindle between two neighboring cells. 



Fig. 16. Longisection of "fingers" of nucleus, showing partition walls partly 

 dissolved. Accessory chromosome twisted like a rope. 



Fig. 17. Cell at a stage similar to above. Nucleus showing irregular dissolu- 

 tion of partition, forming a number of larger vesicles. 



Fig. 18. Cross-section of "hand" of nucleus, showing ends of spiremes. 



Fig. 19. Longisection of sacculations of nucleus. 



Fig. 20. Late prophase. Nuclear membrane dissolved. Chromosomes of a 

 homogeneous structure. Centrosome and aster in lower right-hand corner. 



Fui. 21. Prophase just before division. Chromosomes moving toward equatorial 

 plate. Nuclear membrane dissolved. Accessory chromosome still enclosed 

 in its membrane and granular in structure, while the others are homogene- 

 ous. At <t is drawn an accessory chromosome with its membrane from an- 

 other cell of the same cyst. It is split longitudinally and twisted like a 

 two-strand rope. 



Fi(i. 22. Metaphase of secondary spermatogonium. Accessory chromosome in- 

 distinguishable from its mates. 



Fig. 23. Polar view of metaphase. Chromosomes divided and ready to be drawn 

 apart. Clear areas filled with karyoplasm may be seen around the different 

 chromosomes. 



Fig. 2'±. Anaphase. Accessory chromosome distinguishable by its greater 

 length and rougher contour. 



Fk;. 25. Anaphase, showing elliptical course traversed by the chromosomes in 

 their course toward the poles. 



Fig. 26. Early telophase, showing connecting fibers forming a cylinder. 



Fig. 27. Later telophase. Masses of chromosomes have moved much farther 

 apart than were the centrosomes in the metaphase. Connecting fibers form 

 a hyperboloid, and each has developed on it at the point where it pierces the 

 partition wall a email but deeply staining enlargement. 



