FIG. 34. Photomicrograph of early spireme stage of first spermatocyte, showing peripheral position of the accessory chromosome _x_. At the left, secondary spermatogonia, last generation. × 1300. FIG. 35. A late prophase, showing accessory chromosome _x_, and spindle remains _s_ (_cf._ figs. 3 and 4). × 1300. FIG. 36. Coarse spireme of first spermatocyte. × 1300. FIG. 37. Prophase, with chromosomes in the form of long segments. At _a_, the cell drawn in figure 9. In the cyst at the left are spermatocytes in a later stage, with the chromosomes homogeneous. × 1000. FIG. 38. Prophase with segments divided longitudinally and across. At _a_ is one shown _en face_. Accessory chromosome at x. × 1000. FIG. 39. Metaphase and anaphase of first spermatocyte. The accessory chromosome _x_ at one pole of the spindle. Lagging chromosome at _c_. × 1300. [Illustration: Spermatocytes] Explanation of Plate X. FIG. 40. Anaphase of first spermatocyte. Accessory chromosome _x_ at one pole. The form of chromosome in the anaphase well shown. The lagging chromosome _c_ seen in two cells. × 1300. FIG. 41. Anaphase of the first spermatocyte, showing the longitudinally divided condition of the accessory chromosome _x_ in the cell near the center. Compare with the accessory chromosome in the metaphase of second spermatocyte, figure 43. × 1300. FIG. 42. Second spermatocyte in metaphase. In most of the cells the focus is upon the ends of the chromosomes, but in one a side view is obtainable. Compare with the chromosome of the upper cell in figure 40. No accessory chromosome in most of the cells in focus. × 1300. FIG. 43. Second spermatocyte metaphase and spermatids. Note the relative sizes of the accessory chromosome and the other chromosomes. In the spermatids the accessory chromosome has taken its place on the periphery of the nucleus in the same way that it does in the prophase of the first spermatocyte. × 1300. FIG. 44. Anaphase of the second spermatocyte, showing the accessory chromosome _x_ separated. Other cells in metaphase. × 1300. FIG. 45. Telophase of the second spermatocyte. Two daughter-cells with persisting spindle between, showing the accessory chromosome _x_ in each. Other nuclei in focus show no accessory chromosomes. × 1300. [Illustration: Spermatocytes] ------------------------------------------------------------------------ TRANSCRIBER’S NOTES 1. Silently corrected obvious typographical errors and variations in spelling. 2. Retained archaic, non-standard, and uncertain spellings as printed. 3. Enclosed italics font in _underscores_. 4. Enclosed bold font in =equals=. 5. Denoted superscripts by a caret before a single superscript character.