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. [Illustration: PLATE II.] Explanation of Plate III. FIG. 27. This shows the nebenkern elongating. The axial filament passes over its surface. FIG. 28. A little later than fig. 27. FIG. 29. Shows cross-sections of elongating nebenkern; _a_ shows axial filament, nebenkern and acrosome; in _b_ the axial filament is cut at an angle. FIG. 30. A little later than fig. 28; the axial filament not so plainly shown. FIG. 31. The ring has disappeared, and the dark mass is passing down along the filament. The acrosome is indistinct. FIG. 32. The nebenkern has disappeared, but the acrosome has kept its position. FIG. 33. The acrosome has flattened against the nucleus. Some remains of the nebenkern are seen. FIG. 34. The acrosome has moved to the side of the nucleus. Some nebenkern remains are shown. FIG. 35. The acrosome is in front of the nucleus. FIG. 36. A little later stage than fig. 35. FIG. 37. Shows a divided acrosome. It is not a frequent appearance. FIG. 38. The nebenkern appears as a hanging drop on the side of the axial filament. FIG. 39. The nucleus has condensed, the walls have thickened, and the chromatin appears in granules. The acrosome is pointed. FIG. 40. A little later stage than 39. FIG. 41. A little later stage than 40. FIG. 42. The head is stained intensely, while the acrosome is lighter. Probably a middle piece indicated. FIG. 43. The head shows the clear space.