PLATE XVI. 



Drawings made at a magnification of 22r.o. In reproduction this has been reduced to 



1800 diameters. 



Fig. 1. — Spermatogonium, showing twenty-three chromosomes. 12, the 

 largest chromosome of the complex; 1, the smallest; 9, a chromosome 

 showing the longitudinal split. 



Fig. 2. — Prophase showing the accessory smooth in outline and darkly 

 staining; 4, a chromosome exhibiting the true tetrad character; 12, 

 the largest chromosome. • 



Figs. 3a and 3b. — A single cell showing the full number of chromo- 

 somes in a first spermatocyte metaphase in lateral view. 



Figs. 5, 6, 7. — Polar views of first spermatocytes, showing the occur- 

 rence of the single ring. 



Fig. 8. — Prophase. Chronjosome 12 in the form of a cross. 



Fig. 9. — Polar view of the first spermatocyte, showing three rings. 



Figs. 10a and 10b. — First spermatocyte metaphase, with the chromo- 

 somes numbered in the order of their size: No. 10, the ring in profile; 

 No. 6, the accessory. 



Fig. 11. — Early anaphase of the second spermatocyte, showing the sepa- 

 ration of paternal and maternal elements. 



Fig. 12. — The chromosome complex of a first spermatocyte, showing the 

 graduated series of chromosomes. 



Fig. 13. — A polar view of the second spermatocyte, with eleven chromo- 

 somes. The accessory is absent. 



Fig. 14. — A polar view of the second spermatocyte, showing the full num- 

 ber of chromosomes. 



