Plate I. 



(^Spermatogenesis . ) 



Fig. I. Longitudinal section of an early testis, showing various 

 generations of spermatogonia in rest and in division. Magnifica- 

 tion : Obj. D (Zeiss) x 4.0c. 



Figs. 2-61. Were all drawn under the same magnification : Zeiss, 

 homog. immersion 1.5 mm. Ap. 1.30 X 12 compens. ocular, tube- 

 length, 160 mm. 



Fig. 2. Cross section of metaphase, early generation of sperma- 

 togonia showing V-shaped chromosomes. 



Figs. 3-6. Longitudinal section of late prophase and metaphase 

 of same showing attachment to the spindle. 



Fig. 7. Middle anaphase of early spermatogonium. 



Fig. 8. Telophase of same showing dense crowding of chromo- 

 somes. 



Figs. 9-1 i. Longitudinal sections of prophase and metaphase of 

 last spermatogonial generation showing rod-shaped chromosomes. 



Fig. 12. Cross-section, of metaphase of the same. 



Figs. 13-14. Early anaphase of last spermatogonial division. 



Fig. 15. Late anaphase of same. 



Fig. 16. Early telophase showing the union of the individual rod 

 chromosomes into pairs. 



, Figs. 17-18. Late telophase where the synapsis has already 

 occurred. 



Fig. 19. Earliest spermatocyte showing the newly formed biva- 

 lents moving apart. 



Fig. 20. Somewhat later stage chromosomes showing marked size 

 differences. 



Figs. 21-22. First traces of longitudinal split. 



Figs. 23-24. Opening up of the angle of the longitudinally split 

 bivalents. 



Fig. 25. Sister bivalents united at their both ends to form the 

 elongated rings. 



Fig. 26. Somewhat later stage than preceding. Chromosomes 

 beginning to concentrate and showing the other type of double rod 

 in which longitudinal split is obscured. 



Figs. 27-30. Further stages in concentration in preparation for 

 1° maturation division showing rings and double bars side by side. 



(59) 



