and
form this element resembles the accessory chromosomes described by
Baumgartner ('04) for _Gryllus domesticus_; in its mode of origin it
seems to differ from the other accessory chromosomes yet described.

Figures 69 and 70 show the 23 bivalent chromosomes in metaphase; in
figure 69 the element _x_ is shown partly behind the large chromosome
and at a different level. In figures 66 and 67 the one exceptionally
large chromosome doubtless represents the two larger ones of the
spermatogonia. In the anaphase the element _x_ is sometimes as
conspicuous as in figure 71; in other cases it is concealed either
behind or within the polar mass of chromatin. In this form there is a
distinct resting stage between the two maturation mitoses (figs. 72-75).
The element _x_ is conspicuous in one-half of the cells (figs. 72, 73);
it may be included in the nucleus as in figure 72, or it may be partly
or wholly outside, as in figures 74, 75, and 76. In the latter case, but
not in the former, it is surrounded by its own membrane. As the
chromatin begins to condense for the second mitosis, disintegration of
the element _x_ becomes apparent. This is most easily made out in cases
where the element is isolated, as in figures 75 and 76; but there seems
to be little doubt that it disappears before the metaphase of the second
maturation mitosis. It is not possible to count the chromosomes in this
stage, they are so crowded together, but it is not probable that such a
conspicuous chromatin element as that seen in the first division could
escape detection, even if it were in the equatorial plate among the
chromosomes. No aberrant element is ever seen in these spindles; and,
moreover, all of the spindles and all of the spermatids appear to be
exactly alike at the same stage. The chromosomes are double in the
prophase (fig. 77) and always appear double in the equatorial plate
(fig. 78), the paired elements corresponding to those of figure 65.

In figure 80, plate III, a pair of spermatids is shown with nuclear
membrane formed and the spindle fibers twisted in a characteristic
manner. Figure 81 is a slightly later stage with the spindle-remains
massed against the nuclear membrane. Curiously enough there appears in
the nucleus of every spermatid a body similar to the element _x_ of the
spermatocytes of the first order (figs. 82-86). This body is often
applied to the nuclear membrane and connected with the spireme (figs.
84-86). It decreases in size