MUNSON: SPERMATOGENESIS OF PAPILIO. 
87 
22. The tetrad formation and the following diad formation lead 
to a gradual orientation of the nuclear material with reference to the 
asters and centrosomes. 
23. The vacuole-like appearance of the nucleus in the spireme 
stage may he due to withdrawal of the linin into the chromosomes. 
24. The spindle is formed from the nuclear contents. 
25. The entire transformation of the nucleus, including the 
spireme and tetrad formation, into a spindle is accomplished after 
the large asters are fully formed. 
26. The nuclear membrane disappears when the first traces of 
the spindle appear- 
27. The occasional indentation of the nucleus where it is in con¬ 
tact with the aster, is not due to the growing out of the astral fibers, 
nor does it seem proper to say that the spindle fibers grow into the 
nucleus and become attached to the chromosomes. 
28. The chromosomes are gradually drawn into the equator of 
the spindle as the latter is being formed. 
29. The chromosomes divide but as they are spherical, it is absurd 
to speak of a longitudinal or a transverse splitting of these chromo¬ 
somes. 
30. The tetrads are formed from separation of the four chromo¬ 
somes lying side by side in the doubly folded spireme. 
31. There is in maturation only one case of undoubted division 
of a chromosome — the splitting of the equatorial plate in the first 
maturation division. 
32. The first maturation division is an equation division, one 
half of each chromosome being drawn toward its respective pole. 
33. The second maturation division sometimes begins before the 
first has been completed. 
34. The spindle in the second maturation division differs from 
that of the first in that only the central fibers are connected with the 
chromosomes, and in that no equatorial plate is formed. 
35. The second maturation division results only in a sorting; of 
the chromosomes, fourteen being drawn toward one pole, fourteen 
toward the other. 
36. It might be thought that the diads in the first maturation 
division fuse, were it not that sections through the equatorial plate 
show twenty-eight chromosomes, the somatic number. 
37. I infer, therefore, that each spermatid receives one half the 
