(_a_) THE NUCLEUS.
The chromatin in _Gryllus_ behaves very much as Henking (’91) has
described for _Pyrrhocoris_, and Paulmier (’99) for _Anasa_. At the
end of the anaphase the chromosomes are crowded together at the
poles of the spindle. (Fig. 1.) A clear space begins to be formed
around them, especially on the equatorial side. (Fig. 2.) They then
separate and are scattered somewhat evenly over the nuclear membrane
when it is formed, as seen in figs. 4, 5, and 6. Soon protuberances
appear on the surface of the individual chromosomes, making their
outlines irregular. At about this time they begin to show a granular
structure. The chromosomes break up more and more, and soon the
chromatin appears in irregularly arranged patches or blotches of
granules of various sizes. (Fig. 8.)
Meanwhile the nucleus has slowly increased in size. It reaches its
maximum, which is probably about treble its original diameter,
before the cell begins to elongate. The granules have been breaking
up into finer and finer pieces, until, a little after the cell has
reached its maximum, the chromatin has largely disappeared, or, to
be more exact, has lost its affinity for stains. (Fig. 16.) As the
cell begins to elongate, the nucleus goes to one end, namely, that
toward the periphery of the cyst. (Figs. 14 and 15.) The chromatin
again frequently appears in patches as the cell decreases in size.
(Figs. 33 and 36.) In many cells the patches never disappear. When it
has diminished to less than half its maximum diameter, the nucleus
begins to elongate, becoming elliptical, and finally forms the long,
tube-like head of the spermatozoon. (Figs. 43 and 45.)
I found here that the nucleus was hollow, or, better, that it
showed a clear space within. For a long time it contains the many
chromatin granules, as seen in figs. 39, 40, and 41; but at last the
walls seem to attract all these granular masses, and the center is
entirely clear, as in fig. 45. In fig. 44 are shown cross-sections
of spermatozoa heads, of the stage of fig. 43. In fig. 45 we have a
mature spermatozoon head.
The _accessory chromosome_ in _Gryllus_ lags behind during the
spermatogonial divisions, just as in _Xiphidium_ (McClung, ’99),
and retains its identity all through the growth period, in many
cases becoming quite large. At first it cannot be distinguished
in the spermatid, but soon its stronger stain and exemption from
disintegration make it apparent. (Fig. 4.) It is flattened against
the nuclear wall and, unlike Paulmier’s “small chromosome,” it
does not break up but remains intact, as Henking and McClung have
described. (Figs. 14, 18, 32, 37, and others.) It gets larger and
then smaller, and is finally lost in the rest of the chromatin, as
the latter condenses to form the spermatozoon head. I was not able
to see that it occupied one side of the elongating head, as McClung
describes it in _Xiphidium_. The darker stain and regular contour,
and sometimes its greater size, made it in most stages quite evident.
(_b_) CYTOPLASMIC STRUCTURES.
It is in the cytoplasmic structures that _Gryllus_ shows some things
that have not been described, so far as I know; yet I almost hesitate
to enter the discussion concerning the nebenkern, the mitosome, the
idiozome, the archoplasm, the attraction sphere, the acrosome, the
“mitochondrion körper” and other bodies which have been described in
the extra-nuclear parts of the germ-cell. But because I have been
unable to find in any of the papers a description of a structure
like the one in _Gryllus_, I shall proceed to describe the nebenkern
as I find it. I shall interpret the appearances as far as possible,
leaving to others, or to later efforts, the complete harmonizing of
this element with the structures of other species.
Before I proceed, I would add my protest against the name
“nebenkern,” as voiced by Calkins (’95), Erlanger (’96), Meves (’00),
and others. It is inapt and not at all descriptive or distinctive.
But since we have the word, and investigators will use it to mean
something, I think it would be best to restrict the word, as Calkins
and Erlanger suggest, to the remaining spindle fibers and connective
fibers which go to each spermatid and which have an important part
in forming the tail membrane. I shall retain the name for a further
reason, which St. George (’97) gives for first using it, “weil
sie die Frage nach der Herkunft dieses Gebildes offen lässt.” A
comparison of the literature will convince any one that the origin of
this element is still a much-disputed question.