Explanation of Plate II.

All drawings were made by the author with the aid of a camera lucida. All figures except 2, 3, 4 and 45 were made with a B. & L. ¹⁄₁₆ objective and one inch eye-piece, producing a magnification of 1340 diameters. Figs. 2, 3, 4 and 45 were drawn with a Leitz ¹⁄₁₆ objective and a Zeiss compensating ocular No. 12, giving a magnification of 2325 diameters. The drawings were not reduced in the photo-mechanical reproduction.

Fig. 1. An early telophase, in which the fibers appear like barrel staves. Some of the fibers have thickened.

Fig. 2. A later stage, in which the fibers are uniting, the clear space is forming, and the chromosomes are beginning to separate.

Fig. 3. A daughter-cell, showing the chromosomes separating and the fibers thickening.

Fig. 4. The chromosomes are scattered over the nuclear membrane; the fibers appear as a few thick rods. The beginning of the acrosome is seen. The accessory chromosome can be distinguished.

Fig. 5. Same as fig. 4, with some of the fibers curved and no acrosome.

Fig. 6. Same as fig. 5, but with the acrosome visible.

Fig. 7. The chromosomes are granular; the fibers have bent and formed the round “striated nebenkern.” The acrosome is present.

Fig. 8a. Same as fig. 7, but the acrosome is not present.

Fig. 8b. The fibers run parallel with the long axis of the nebenkern.

Fig. 9. Here is shown a partial end view of the nebenkern. The accessory chromosome and the acrosome are both prominent.

Fig. 10. The nebenkern shows some of the fibers on the under side. It is beginning to break up.

Fig. 11. The nebenkern shows the beginning of the dark center; the fibers extend from it to the ring. The acrosome has a peculiar appearance.

Fig. 12. The fibers have broken up and the whole has assumed a vesicular appearance, resembling a blackberry. The acrosome is present.

Fig. 13. This shows a persisting spermatid stage. The chromatin appears in patches. The nebenkern is in the ball-and-ring stage. The acrosome shows its characteristic clear center surrounded by a ring darker on one side. The two dark bodies on the nuclear surface are probably artefacts.

Fig. 14. A stage a little later than 13. The dark central ball shows some vacuoles. The cell is beginning to elongate.

Fig. 15. Same as fig. 14, with the ball denser.

Fig. 16. The nucleus has become almost clear. The acrosome is behind the nebenkern.

Fig. 17. This shows the axial filament apparently growing out from the nucleus. There is an aggregation of chromatin at its base.

Fig. 18. The axial filament passes over the nebenkern, which has slightly elongated. The accessory chromosome is very plain.

Fig. 19. a shows a surface view, and b an optical section, of a nebenkern which is in process of breaking up.

Figs. 20 and 21 have part of the surface fibers cut off and show the dark mass forming within.

Fig. 22. Shows a nebenkern passing from the blackberry stage into the ring stage.

Fig. 23. This is an end view of the stage shown in figs. 20 and 21.

Fig. 24. The fainter lines are the fibers on the under side of the nebenkern.

Fig. 25. The blackberry stage, showing the mass of vesicles.

Fig. 26. This represents a nebenkern of the stage shown in fig. 7, drawn from a polar view, with adjusting focus.

PLATE II.