Drawings were made with a _camera lucida_, the optical combination being
a 1–16 B. & L. objective and a Watson “Holoscopic” ocular No. 7. Details
were studied with a Zeiss 2-mm. apochromat, N. A. 1.30. As reduced in
reproduction, an enlargement of 1500 diameters exists. Photomicrographs,
excepting those of figures 37 and 38, were made by the use of the arc
light and horizontal camera. The exceptions represent illumination by
ordinary diffuse daylight. In all cases the lenses used were the Zeiss 2
mm., N. A. 1.30 objective and projection oculars. A Watson
“Parachromatic” oil-immersion condenser of 1.30 N. A. was employed to
illuminate the objects. In use it was stopped down to between .75 N. A.
and 1.0 N. A.
Explanation of Plate VII.
FIG. 1. Pole view of spermatogonial metaphase, showing the thirty-three
chromosomes. It will be observed that the chromosomes are of unequal
sizes, and that the large ones arrange themselves in a circle on the
outside of the figure.
FIG. 2. Very young spermatocyte. The chromatin derived from the breaking
down of the spermatogonial chromosomes in a diffuse condition, with no
trace of a linear arrangement. The accessory chromosome _x_ on the
periphery of the nucleus, darkly staining and homogeneous.
FIG. 3. Early stage in the formation of the spireme. In the cytoplasm
the remains of the spermatogonial spindle. The cell has entered upon the
growth period.
FIG. 4. A later stage in the spireme formation. The accessory chromosome
larger and more flattened. A surface view shows it as an apparently
fenestrated plate. The remains of the two spermatogonial spindles still
persisting.
FIG. 5. First appearance of definite chromosomes. One shown entire with
longitudinal and cross-divisions marked. The accessory chromosome is
here seen to be in a spireme condition.
FIG. 6. Condition of the chromosomes after further contraction of the
early segments. As here shown, they are more granular than is usually
the case.
FIG. 7. Common types of the prophase chromosomes.
FIG. 8. A cell in which one of the chromosomes has its halves widely
separated along the longitudinal division, forming Paulmier’s double-V
figure.
FIG. 9. In this cell may be seen the variation in form and size of the
early spermatocyte chromosomes.
FIG. 10. Two cells of the late prophase, with the chromosomes at almost
the extreme degree of concentration.
FIG. 11. Chromosomes of cells in the stage shown in figure 10. These
represent the different types of rings, crosses, etc., commonly observed
in first spermatocytes just before the formation of the mitotic figure.
FIG. 12. Different forms assumed by the accessory chromosome in the
prophase of the first spermatocytes of _Xiphidium_.
FIG. 13. Metaphase of the first spermatocyte. The accessory chromosome
is seen at one pole of the spindle, to which it has moved before the
separation of the chromatids of the remaining chromosomes.
FIG. 14. Another cell in about the same stage as that represented in the
preceding figure.
FIG. 15. A first spermatocyte metaphase in which the accessory
chromosome has not as yet moved to the pole of the spindle. This is
uncommon in _Orchesticus_, but frequent in _Anabrus_.
FIG. 16. Pole view of a first spermatocyte metaphase, showing seventeen
chromosomes. The variation in size of the elements, so marked in the
spermatogonia, is even more pronounced here. This is a cell similar to
that of figure 15, in which the accessory chromosome lies in the
equatorial plate.
[Illustration: Spermatocytes]
Explanation of Plate VIII.
FIG. 17. Two cells in metaphase—a pole view of one and an oblique view
of the other. The accessory chromosome does not show in the former, the
cell being such a one as is represented in figures 14 and 15.
FIG. 18. Pole view of another cell, showing but sixteen chromosomes.
FIG. 19. Early anaphase of the first spermatocyte, with the accessory
chromosome already at one pole.
FIG. 20. Mid-anaphase, with the giant chromosome still undivided.
FIG. 21. Later anaphase, in which the accessory chromosome is seen at
the lower pole. This figure shows, also, the character and extent of the
intercellular material.
FIG. 22. Later anaphase. The accessory chromosome at the upper pole. An
undivided chromosome lying between the groups of daughter chromosomes.
FIG. 23. About the stage of figure 22, but the lagging chromosome has
divided.
FIG. 24. Very late anaphase. Here, again, the lagging chromosome is
divided.
FIG. 25. Pole view of first spermatocyte telophase, showing the
accessory chromosome at one side of the daughter chromosomes.
FIG. 26. Pole view of a cell in the same stage as that represented in
figure 25. Here, however, the accessory chromosome is not present.
FIG. 27. Lateral view of telophase, with the accessory chromosome in the
lower daughter-cell.
FIG. 28. Fragment of second spermatocyte, showing the chromosomes in
metaphase. The relative sizes of the accessory chromosome and the
remaining chromosomes is well shown.
FIG. 29. Metaphase of a second spermatocyte, in which the accessory
chromosome is not present.
FIG. 30. Anaphase of second spermatocyte, in which there is no accessory
chromosome.
FIG. 31. Anaphase of second spermatocyte, where the accessory chromosome
is present—_x_^1 and _x_^2.
FIG. 32. Telophase of the same class of second spermatocytes. The
accessory chromosome extends out from the mass of chromosomes at each
pole—_x_^1 and _x_^2.
FIG. 33. Telophase of the class of second spermatocytes from which the
accessory chromosome is absent.
[Illustration: Spermatocytes]
Explanation of Plate IX.
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]
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