34 J- E. WODSEDALEK. 



EXPLANATION OF PLATES. 

 PLATE I. 



(Fig. i, X20o; Figs. 2 and 3, Xsoo; Figs. 4-12, Xi,20o.) 



1. Section of a pig testis showing the seminiferous tubules separated by wide 

 areas of interstitial cells. 



2. Section of a tubule showing bunches of developing spermatozoa attached 

 to Sertoli or nurse cells. 



3. Section of a tubule showing almost fully developed spermatozoa which have 

 deserted the Sertoli cells and became scattered among the masses of cast-off cyto- 

 plasm. 



4. Resting stage of a spermatogonial cell showing two large nucleoli. 



5. Primary spermatocyte in the synizesis stage. 



6. Resting stage of a primary spermatocyte showing the two large nucleoli. 



7. Spireme stage of a primary spermatocyte showing the chromatin threads 

 and the two persisting nucleoli. 



8. Late prophase of division in a primary spermatocyte showing eight chromo- 

 somes in the main group, and the two accessories lying off to one side. The 

 photograph does not reveal the full size of the accessories. 



9 and 10. Side views of primary spermatocytes showing the cell ready for di- 

 vision with the accessories lying just above the level of the regular equatorial plate 

 of chromosomes. 



11. Side view of a primary spermatocyte division with the two accessory 

 chromosomes passing to the pole, side by side, in advance of the other chromosomes. 



12. Side view of a primary spermatocyte division showing the two accessories 

 at the pole while the autosomes are still in the equatorial plate undivided. 



13. Two metaphases of secondary spermatocytes showing four chromosomes in 

 the equatorial plate. The figure at the top is a side view, and the one at the bottom 

 a polar view. 



14. The cell at the top is one type of secondary spermatocyte which contains 

 four chromosomes in the metaphase stage and the cell below is a spermatid resulting 

 from the division of a type of secondary spermatocyte which received eight auto- 

 somes plus the two accessories. 



15. Resting stage of a spermatid showing two nucleoli. 



