chromatin stains very dark throughout the growth stage, and the
unequal pair can not be distinguished until the prophase of division
('05, plate VI, figs. 171-180), in most of the others there are very
distinct synizesis and synapsis stages, following the last
spermatogonial mitosis, then a spireme stage in which the condensed
unequal pair of heterochromosomes or the odd chromosome is conspicuous
in contrast with the pale spireme, whether the preparation is stained
with iron-haematoxylin, gentian, or thionin. In _Tenebrio molitor_, the
unequal pair behaved in every respect like the other bivalent
chromosomes. In the other forms, though it behaves during the two
maturation divisions like the symmetrical bivalents, it remains
condensed during the growth period like the "accessory" of the
Orthoptera, the odd chromosome, "_m_-chromosomes," and "idiochromosomes"
of the Hemiptera. In several cases the heterochromosomes of the
Coleoptera are associated with a plasmosome (figs. 22, 23, 63, 132, 158,
217), as is often true in other orders. This peculiar pair of unequal
heterochromosomes varies considerably in size during the growth stage in
some of the species studied, but changes very little in form, differing
in this respect from the "accessory" in some of the Orthoptera (McClung,
'02) and from the large idiochromosome in some of the Hemiptera (Wilson,
'05).

The odd chromosome, so far as it has been studied, behaves precisely
like the larger member of the unequal pair without its smaller mate
(figs. 219, 220, 226, 233). In the growth stage it remains condensed and
either spherical or sometimes flattened against the nuclear membrane
(figs. 217, 225, 231). In the first maturation mitosis it is attached to
one pole of the spindle, does not divide, but goes to one of the two
second spermatocytes (figs. 233, 235). In the second spermatocyte it
divides with the other chromosomes, giving two equal classes of
spermatids differing by the presence or absence of this odd chromosome.

All of the evidence at hand leads to the conclusion that in the
Coleoptera, the univalent elements of all the pairs, equal and unequal,
separate in the first spermatocyte mitosis and divide quantitatively in
the second. In this respect the behavior of the chromosomes in this
order appears to be much more uniform than in the Orthoptera and
Hemiptera.

COMPARISON OF THE COLEOPTERA WITH THE HEMIPTERA AND LEPIDOPTERA.

As has been seen above, the c