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Explanation of Plate XX, 
All figures were drawn with apochromatic immersion, lens apert. 1.35, and com- 
pens.-oc. 8 (magnification about 1275). 
Fig. 1. The resting nucleus. 
Fig. 2. The homogeneous reticulum. 
Fig. 3. The same becoming thicker. 
Fig. 4a and 6. Breaking down of cross-connections to form the spireme. 
Fig. 5. Early spireme, the edges still ragged. 
Fig. 6. Flat ribbon-shaped spireme. 
Fig. 7. The spireme split longitudinally. 
Fig. 8. Segmentation of spireme. 
Fig. 9. Same showing early spindle. 
Fig. 10. Spireme completely segmented. 
Fig. 11. Chromosomes passing on to spindle. 
Fig. 12. Chromosomes beginning to split. 
Fig. 13. Fission completed. 
Fig. 14 and 15. Metaphase. 
Fig. 16. Early anaphase with segmented chromosomes. 
Fig. 17. Late anaphase. 
Fig. 18. Telophase, cliromosomes contracted. 
Fig. 19a and 5. Chromosomes uniting end to end, and putting out lateral cross 
Connections. 
Fig. 20. Later stage of same. 
Fig. 21. Reticulum reconstituted. 
Fig. 22. Polar view of telophase — paired cliromosomes. 
Fig. 23 and 24. Polar view of telophase. 
