There are, in _Gryllus_ spermatids, two quite permanent and prominent
extra-nuclear bodies. The larger of these I shall call _nebenkern_,
because I believe it originates from the spindle remains, and goes to
form the tail covering. Its behavior is as follows: At the beginning
of the telophase the fibers which had connected the centrosomes with
the chromosomes bulge out like barrel staves, as Henking (’91) has
described. These break loose from the chromosomes and centrosomes
as the clear space begins to form around the chromatin mass (fig.
2); but they are not separated into two rings, as in _Anasa_
and _Pyrrhocoris_. As the dividing cell membrane is formed, the
middle portions of the fibers are drawn together and the so-called
“mid-body” is formed. Some of the fibers unite, producing thicker
ones, as seen in figs. 1, 2, and 3. In the last-named figure some
of the central fibers seem to be still united with those of the
companion spermatids.
As the daughter-cell shortens and the nucleus takes a more central
position these fibers unite still more, shorten, bend together (figs.
4, 5, and 6), and finally assume the shape shown in fig. 7. I shall
call it for the present the “striated condition,” or simply “striated
nebenkern.” The shape resembles that of an egg with rather sharply
drawn-out ends. The surface is occupied at intervals with deeply
staining lines which look much like hoops. In most cases the long
axis of the nebenkern is at right angles to the axis of the spindle
from which it was formed, while the striæ, or dark lines, are in
planes parallel to it, as is seen in figs. 7 and 8_a_. In a few cases
the lines are parallel to the long axis of the nebenkern, as shown in
fig. 8_b_. Fig. 9 exhibits a partial end view of the nebenkern, while
fig. 26 represents a polar view in all planes.
The fibers in figs. 4 and 5 are not all in the same plane, giving
frequently, with changing focus, the impression that the lines are
the edges of plates. Even in figs. 7 and 8, the appearances shown
made me hesitate for some time before I dared say that the lines
represent striæ on the surface and not plates extending through the
body. But the end views (figs. 9 and 26) and the two drawings in fig.
19 show clearly that we are dealing with encircling hoops and not
dividing plates. Just how or why the fibers bend and assume the shape
of figs. 7 and 8 I am not able to say, but I am sure it is not an
artefact, as might be supposed, because I have found them occupying
whole cysts of several testes, and nearly all of them were as regular
and definite as fig. 7.[A]
I have found the nebenkern in its perfect condition (fig. 7) only in
material fixed in Flemming; although Zenker’s fixation showed some of
the breaking-up stages. This may be due partly to poorer fixation in
other mixtures and partly to chance, as not so many testes fixed in
other agents were examined, and the appearance evidently represents
a very brief stage. These fibers now begin to break up, and we get
figures that remind one of Meves’s “mitochondrion körper”; that is, a
darker staining center and radiating lines to the outer ring. (Fig.
11.) Sometimes stages a little later recall Paulmier’s “blackberry
stage.” (Figs. 12 and 25.) Fig. 19_a_ is a surface view and fig.
19_b_ an optical section of a nebenkern that is in the process of
breaking up. Figs. 20 and 21 have a part of one end cut off, while
fig. 23 is a polar view. Fig. 22 is probably a forming blackberry
stage.
All the above are brief stages, and we soon get the appearance of
figs. 13-16. Here we have the darkly staining central ball surrounded
by a clear space, enclosed by a ring, as Meves (’00) found it in
_Pygæra_. The central ball sometimes shows vacuoles (fig. 16),
but most frequently stains as one mass. In some cysts with cells
resembling fig. 16, it is difficult to distinguish between nucleus
and nebenkern, yet the latter’s stain is never as intense as that of
chromatin. The stages shown in figs. 13 and 14 persist for a long
time, and it is probable that this is the end of the telophase and
the beginning of the spermatid transformations. I have treated the
above more in detail and shown more drawings than its importance may
deserve, but it is in these stages that _Gryllus_ seems to differ
from other species, and I have tried to describe and illustrate the
appearances and changes fully.
As the cell elongates, the axial filament grows out, the nebenkern
approaches it, and a junction is effected in such a way that the
axial filament runs over the surface of the nebenkern. (Figs. 18,
27, 28, and 30.) At first the nebenkern is still almost round, but
it begins to elongate and the dark inner ball sends out a protrusion
to the nucleus, and sometimes back to the point of separation
between the external envelope and the axial filament. The outside
ring disappears and the dark mass moves down the axial filament.
(Fig. 31.) In many cases it breaks up into several small drops,
which appear at intervals on the axial filaments. (Figs. 34 and 36.)
In fig. 38 is seen such a hanging drop. In this way the nebenkern
material is distributed over the axial filament and forms a sheath
around it.
[A] Professor McClung, Mr. Sutton, and Mr. Blackman, of Kansas
University, and Doctor Child and Mr. Harper, of Chicago University,
have seen my preparations, and all confirm my statement that the
appearance is _not_ an artefact.