5°° 
The Ohio Naturalist. 
[Vol. IX, No. 7, 
THE FIRST NUCLEAR DIVISION OF THE MOTHER-CELL. 
All sixteen chromosomes divide almost simultaneously. To 
determine the plane of this division was no easy task. That it 
is a transverse division is quite evident from the cells examined. 
Figs. 14a, 16a, 16b, show some chromosomes dividing trans¬ 
versely, and since this is the only transverse division, it should 
be considered qualitative. The spindle fibers end near or at the 
free ends of the chromosomes. The homologous daughter 
chromosomes show not only a marked correspondence in size, 
but also in shape (Fig. 14, 14a, 15, 16b). Whether this similarity 
in shape is inherent, or is the result of a stress brought about by 
the spindle fibers, or is the result of a repulsion of the daughter 
chromosomes has not been determined. J, I, V, U, shaped 
chromosomes are present. I and J shaped predominate (Figs. 
15, 16). In rare instances indications of a median cleft through¬ 
out the length of the chromosome in metaphase could be noticed 
(Fig. 14a). This is probably the beginning of the second 
division. Since the daughter chromosomes show such a marked 
similarity in shape, the author was at first skeptical about the 
plane of the division, but enough data are now at hand to prove 
that the division is transverse. Figs. 14a, 14b, 15a, 16a, 16b, 
etc., show this. In the migration of the daughter chromosomes 
to their respective poles, a doubleness is occasionally detectible 
(Figs. 16, 17a). This is probably the beginning of the second 
division. A wall now develops and a distinct nuclear plate is 
seen between the daughter nuclei (Fig. 17). The micronuclei 
apparently re-enter the nucleus (Figs. 17, 18). 
THE SECOND NUCLEAR DIVISION OF THE MOTHER-CELL. 
The daughter nuclei do not enter into a definite period of rest, 
and the chromosomes soon become developed into the mother 
skein of the second division. The transition is so rapid, and the 
telophase of the first division and the prophase of the second are 
so close together, that the individual chromosomes seem to be 
separate from the beginning. Occasionally, a cell is seen in which 
the second division has already taken place, while its sister cell 
is still undivided (Fig. 22). Ordinarily, the sixteen chromo¬ 
somes of each of the two daughter cells of the first division are 
almost immediately ready for the second division. Sometimes a 
cell is seen in which some chromosomes, the double nature of 
which is apparent, lie in a horizontal position in prophase, while 
other chromosomes, which are slightly more advanced, are at 
right angles to the horizontal ones, and are already migrating to 
their respective poles (Fig. 19). There seems to be little prob- 
abilitv that this is a cell in which some chromosomes are dividing 
longitudinally while others are dividing transversely as McClung 
