360 THOS. H. MONTGOMERY, 



Plate 19. 



Fig. 1. Portion of transverse section of testis, showing 6 spermato- 

 gonia in rest stage and the sheath of the testis. 



Fig. 2. Two spermatogonia, rest stage, one shown only in outline. 



Fig. 3. Spermatogonium, beginning of prophase. 



Fig. 4. Nucleus of spermatogonium , dense spirem stage ; with 

 certainly not more than 3 distinct chromatin segments, and probablj^ 

 with only a single one. 



Fig. 5. Spermatogonium, later spirem stage, with not more than 

 3 or 4 chromatin segments. 



Fig. 6. Spermatogonium, lateral view in loose spirem stage ; at x 

 one of the segments showing banded structure. 



Fig. 7. Spermatogonium, segmented spirem; one surface of the 

 nucleus only, showing the chromatin segments terminating against the 

 nuclear membrane. 



Fig. 8. Spermatogonium, lateral view of nucleus in loose spirem 

 stage, most of the segments shown. 



Figs. 9, 10. Spermatogonia, loose spirem stages; in each case most 

 of the segments shown. 



Figs. 11, 12. Spermatogonic nuclei, spirem segmentation nearly 

 completed. Fig. 11 showing 27 chromatin segments. 



Fig. 13. Spermatogonium, completed spirem segmentation. 



Figs. 14 — 18. Spermatogonia, lateral views of a series of stages 

 leading to the formation of the monaster. 



Figs. 19 — 21. Spermatogonia, lateral views of monaster stages. 



Figs. 22 — 36. Spermatogonia, pole views of monaster stages, cyto- 

 plasmic details not shown. 



Fig. 37. Pole views of (A) spermatogonic monaster, and of (B) 

 one cell (1st spermatocyte) of spermatogonic dyaster. 



Fig. 38. Spermatogonium, lateral view of metakinesis. 



Fig. 39. Two chromosomes at the beginning of a spermatogonic 

 metakinesis. 



Fig. 40. Spermatogonium metakinesis, oblique lateral view so that 

 the spindle is not seen. 



Figs. 41 — 46. Spermatogonia, lateral views of a series of meta- 

 kinesis stages, cytoplasmic details not shown. 



Figs. 47, 48. Spermatogonia, lateral views of metaphases; Fig. 48 

 obliquely seen. 



Fig. 49. Spermatogonic metaphase (dyaster) viewed obliquely from 

 one pole, showing 4 chromosomes ; the dotted line shows the region 

 around which the central ends of the other chromosomes are grouped. 



Fig. 50, Spermatogonic dyaster, slightly oblique pole view of one 

 chromosome plate. 



Figs. 51, 52. Spermatogonic anaphases, viewed obliquely from 

 one pole; in Fig. 51, 4 chromosomes, in Fig. 52, 6 chromosomes shown; 

 the dotted line as in Fig. 49. 



