d
a much larger mate. In the prophase of the spindle, in rare cases, some
of the chromosomes are longitudinally split and transversely
constricted, forming tetrads (fig. 180), but more often they appear as
in figure 181. The unequal pair appears in each figure at _s_. In the
metaphase (fig. 182) it is the last to come into the equatorial plate,
possibly because of its lack of symmetry. The smaller component of this
pair is always directed toward the equator of the spindle. Figure 183
shows a small tangential section of a spindle in metaphase, containing
the unequal pair and one equal pair. In figure 184 a polar view of a
metaphase is shown, the unequal pair, which was somewhat below the
others, being indicated by stippling. Figures 184 _a_ and 185 show that
the unequal components of the unsymmetrical pair, as well as the equal
components of the symmetrical pairs, are separated in metakinesis,
making this clearly a reduction division. Two polar plates are shown in
figures 186 and 187, one containing 10 equal elements, the other 9 equal
ones and 1 small one. The telophase is shown in figure 188. There is no
resting stage, but the new spindle is formed from the remains of the old
one, and the spindle-shaped mass of chromatin seen in figure 188 either
passes into the center of the new spindle or becomes enveloped by it.
The double chromosomes separate as in figures 189 and 190. Figure 190
shows the small dyad, and figure 189 an aberrant one which may be its
mate. The spindle in both divisions is peculiar in having outside of the
spindle proper a dense mass of fibers which, in osmic material, stain
deeply with iron haematoxylin. These fibers are shown in all the figures
from 174 to 196. Figures 191 and 192 are equatorial plates of the two
kinds of spermatocytes of the second order, figure 191 showing the small
chromosome. An early anaphase appears in figures 193 and 194, which show
both the small and larger chromosomes in metakinesis. Figure 195 is a
later anaphase containing the divided small chromosome. In figure 196
are shown the two polar plates of a spindle corresponding to that of
figure 195, and in figure 197 the polar plates of a spindle in which 10
equal chromosomes have been divided. In _Tenebrio molitor_ the
spermatids are therefore certainly of two distinct kinds, so far as the
chromatin content is concerned.

In most of the young spermatids, after the nuclear membrane has formed,
there appears an isolated chroma