DESCRIPTION OF PLATES. 



All figures were drawn from camera-lucida outlines made with a B. and L. i/12-inch oil-immer- 

 sion objective and a i-inch B. and L. ocular. The length of the tube for all drawings was 160 mm., 

 and the drawing-surface of board was 255 mm. below the level of the stage. The initial magnification 

 thus obtained was 1,750 diameters. All drawings have been reduced one-third in reproduction. 



PLATE i. 



FIG. I. Primary spermatogonium \vith two nuclei. Nucleus at right contains a large 

 karyosome. Binucleate condition is due to amitotic division, which is 

 frequent among these cells. The cell is attached to the attenuated follicular 

 wall, which contains broad, elongate, flattened nuclei. 



FIG. 2. Resting-stage of primary spermatogonium, showing chromatin arranged in 

 clumps connected by delicate linin threads. Quantity of cytoplasm small. 

 Contour of nucleus appears somewhat lobed. Primary spermatogonial cells 

 have no nucleoli. 



FIG. 3. Nucleus of cyst membrane of a spermatocyst, similar to that of the resting 

 primary spermatogonia. Division is usually mitotic, but frequently amitotic. 



FIG. 4. Resting-stage of primary spermatogonium with fine-meshed nuclear reticulum 

 containing one large and numerous small karyosomes. Amount of cyto- 

 plasm very scant. 



FIG. 5. Late prophase. The chromosomes are in the stage of a partially segmented 

 and longitudinally split mossy spireme. 



FIG. 6. Still later prophase. The chromosomes are disposed as very slender split 

 rods, some of which are greatly elongate. 



FIG. 7, 8. Equatorial plates of primary spermatogonial mitosis; 35 chromosomes. (The 

 larger number of elements 40 and 37 respectively due to cross-section 

 of limbs of U-shaped chromosomes.) 



FIG. 9. Late metaphase. 



FIG. 10. Anaphase. 



FIG. ir. Late telophase; chromosomes in form of long, mossy, pale-staining threads. 

 Mid-body appears as a very conspicuous structure of fine, deep-staining 

 granules. The daughter-cells are inclosed by cyst-wall of mother-cell. 



FIG. 12. Prophase and late telophase of secondary spermatogonium. The investing 

 wall is that of the mother primary spermatogonial cell in form of a cyst 

 membrane. 



FIG. 13. Resting-stage of secondary spermatocyte. Nuclear reticulum only very slightly 

 chromatic. A distinct chromatin nucleolus (" chromosome nucleolus " 

 " accessory chromosome ") is present. 



FIG. 14. Early prophase. The nuclear reticulum contains numerous karyosomes and a 

 chromatin nucleolus which evidences a bipartite structure. 



FIG. 15. Late prophase; spireme has segmented into a number of mossy lightly-staining 

 chromosomes. The accessory chromosome has retained its sharp contour 

 and deep-staining capacity. 



FIG. 16. Still later prophase ; chromosomes in form of delicate split rods. 



FIGS. 17, 18. Equatorial plates of secondary spermatogonia with 35 chromosomes. 

 Accessory chromosome indistinguishable from the ordinary chromosomes. 



FIG. 19. Equatorial plate of a dividing cell of follicle of a young egg, showing 36 

 chromosomes. 



FIG. 20. Equatorial plate of secondary spermatogonium, showing five of the chromo- 

 somes U-shaped. 



FIG. 21. Cyst showing three cells at metaphase and a fourth partially at early anaphase. 



FIGS. 22, 23. Late telophase ; the pair of lagging chromosomes at left may be the acces- 

 sory ("special chromosome" de Sinety) chromosomes. 



FIG. 24. Telophase of a binucleate cell. Ensuing divisions give rise to spermatocytes 

 with double the usual number of chromosomes (i. e., 2 X 17 ordinary + 2 

 accessory chromosomes) and eventually to giant spermatids and sperma- 

 tozoa. The binucleate condition is probably due to an early amitotic 

 division of the nucleus. 



33 



