XPLANATION OF PLATES. 



All drawings are from camera-lucida outlines, taken with a r B. and L. one- 

 twelfth inch oil immersion objective and one-half, three-fourth, i inch B. and L. 

 oculars. In reproduction a reduction of one-sixth has taken place. 



EXPLANATION OF PLATE II 



FIG. I. V 2,000. Spermatogonium in late prophase, about the time of the 

 breaking down of the nuclear-membrane. The chromosomes, 37 in number, are 

 spread over the central region of the cell. All are of a slightly granular consistency, 

 except one, the accessory chromosome, which is homogeneous. 



FIG. 2. X ijOOO. Division of the last Spermatogonium. (a) Chromosomes 

 arranged on periphery of spindle or (t>] scattered across equatorial plate, (c) Divi- 

 sion figures typical. Centrosomes at apices of spindle. (</and^) Early and late 

 anaphases. 



FIG. 3. X 1,000. Late telophase of last Spermatogonium. All chromosomes 

 except accessory have become granular and lengthened into threads. The accessory 

 is stiil homogeneous. 



FIG. 4. X l,ooo. Early spermatocyte. Chromatin segments beginning to form 

 the karyosphere. The remaining segments scattered over nuclear area, in the form 

 of long, granular threads. Growth period commenced. 



FIG. 5. X 1,000. Later stage. Karyosphere becoming larger. Remaining seg- 

 ments of chromatin spread over the nuclear area in the form of very diffuse masses. 



FIG. 6. X 1,000. Chromatin almost all in the karyosphere. Metaplasm bodies 

 spread through the nucleus in considerable quantities. A less amount in the 

 cytoplasm. 



FIG. 7. X looo. Cell of mature size ready for the prophase. Karyosphere 

 shows no differentiation. Metaplasm bodies decreased in amount. Network in 

 cytoplasm is finer and stains more densely than that of nucleus. 



FIG. 8. X I ,5- Karyosphere as seen in various stages, (a) During early 

 growth period. (^) Just preceding the active prophase. Shows slight differentia- 

 tion. Several vacuoles present in the matrix of spongy chromatin (<-) Karyo- 

 sphere of same stage, showing the chromatin massed in more definite areas, (nf, <?) 

 Very early prophases. Chromatin has become less densely massed ; vacuolar sub- 

 stance has increased in amount ; and has aggregated into one or several large vacu- 

 oles. (/) Part of chromatin has left the karyosphere. (g) Later stage. But little 

 chromatin remains within the karyosphere, and this is massed about the large central 

 vacuole. (/) All chromatin has left the karyosphere except one chromosome, which 

 is probably the accessory. (/, k) Stages in the disintegration of the karyosphere, 

 after the chromatin has all emerged. 



FIG. 9. ]' 1,500. Early prophase. Chromosomes just commencing to leave the 

 kaiyosphere. Cloud-like masses of achromatic matter beginning to arise in the 

 nuclear area. 



FlG. 10. X I )5- Later stage in prophase. Chromatin segments granular and 

 in the form of split threads. 



178 



