and finally disappears (figs. 88-91). The
spindle-remains divides (fig. 83), and a small part of it (_a_) goes to
form the acrosome at the apex of the head (figs. 85-92). The larger part
is probably utilized in the formation of the tail, for it gradually
disappears as the tail develops.

The centrosome which, although small, is conspicuous in each mitosis, is
seen in figure 83 between the two parts of the spindle-remains, applied
to the outside of the nuclear membrane. In figures 85, 86, and 87 the
relation of the tail (or its axial fiber) to the centrosome is shown. In
figures 87 and 88, instead of the small spherical centrosome of figures
83 to 86, we have a much elongated body, at first (fig. 87) applied for
its whole length to the nuclear membrane, but later lying along one side
of a middle piece (_m_), as shown in figure 89, and in a later stage in
figures 90 to 92. The mature spermatozoon with its forked anterior end
appears in figure 93.

The points of especial interest in the spermatogenesis of
_Stenopelmatus_ are the development of the aberrant chromatin element
_x_ during the growth stage of the spermatocyte of the first order, its
distribution to one-half of the spermatocytes of the first order, its
disappearance during the rest stage between the two maturation
divisions, and the development of a similar, though smaller, element in
all of the spermatocytes.

Blattella germanica.

Unlike the spermatogonia of _Stenopelmatus_, those of _Blattella_ have
both a faintly-staining nucleolus and a deeply-staining chromatin
element (_x_), and moreover the two are always closely associated (figs.
95, 96). The number of chromatin elements in the equatorial plate of
late spermatogonial mitoses is 23 (fig. 97). Later events indicate that
one of the 23 is the element _x_, but it is impossible to distinguish it
here. Figure 98 is a very early stage of the spermatocyte of the first
order, showing the element _x_ as a U-shaped body. The centrosome was
also conspicuous in all of the cells of this group. The spireme here, as
also in figure 99, is fine and closely interwound. In figure 99 and
again in figure 100 the element _x_ is joined to the spireme as it is
throughout the spireme stage. In the "bouquet" or "polarized" stage the
combined nucleolus and element _x_ are always at one side of the group
of loops and down very close to the base of the figure (figs. 101, 103).
In figure 102 most of the loops are cut across. The