he character of the
chromatin of one-half of the spermatozoa, though it may not usually be
indicated by such an external difference in form or size of the
chromosomes as in _Tenebrio_. It is important that related forms should
be studied in order to ascertain whether the same chromatic conditions
prevail in other species of this genus or possibly in the Coleoptera in
general.[A]

[Footnote A: Prof. E. B. Wilson has recently found a similar dimorphism
in the spermatozoa of _Lygaeus_ and other of the _Hemiptera
heteroptera_.]

Aphis oenotherae.

The spermatogenesis of _Aphis_ has been fully described in another paper
and will merely be briefly summarized here for the purpose of comparison
with other forms.

The spermatogonia contain a large nucleolus, which gradually disappears
in the prophases of mitosis (plate VII, figs. 209-211). The youngest
spermatocytes closely resemble the spermatogonia (fig. 212). There is no
bouquet stage and no such marked spireme stage as in many other
insects. The true synapsis occurs, as shown in figure 213, by pairing of
like chromosomes side by side. This conjugation of like chromosomes is
followed by a stage in which they are massed together at one side of the
nucleus (fig. 214). In these latter stages the nucleolus has entirely
faded out and nothing suggesting an accessory chromosome is present.
Figures 215 and 216 are equatorial plates of the first spermatocyte
mitosis. There are 5 chromosomes of different sizes and shapes, and
figure 216 shows each one double. The first division of the chromosomes,
though apparently longitudinal, is evidently a separation of the
elements paired in a preceding stage, and is therefore a reducing
division.

The anaphase of the same mitosis is shown in figures 217 and 218; it is
peculiar in that one chromosome always divides more slowly than the
others, the two elements hanging together at one end. In figure 219 are
sister spermatocytes of the second order, the "lagging" chromosomes
still connected. The second maturation division is seen in metaphase in
figure 220 and in anaphase in figure 221. Figure 222 shows a young
spermatid, the five chromosomes still preserving their characteristic
form. Figure 223 is the equatorial plate of the first maturation
division of the winter egg, showing the same form and size relations of
the chromosomes as in the spermatocyte divisions. Figures 224 and 225
are equatorial plates of a polar spindle (fig. 224) and