followed
by either Heidenhain's iron-haematoxylin or Hermann's safranin-gentian
staining method (Arch. f. mikr. Anat. 1889). (2) Fixation after Gilson's
mercuro-nitric formula, followed by iron-haematoxylin, Delafield's
haematoxylin and orange G, Auerbach's combination of methyl green and
acid fuchsin, or thionin.

The iron-haematoxylin with either mode of fixation gives by far the most
satisfactory preparations for general study. The other stains were used
mainly for the purpose of distinguishing between heterochromosomes and
plasmosomes in resting stages of the nucleus.

COLEOPTERA.

Trirhabda virgata (Family Chrysomelidae).

Two species of _Trirhabda_ were found in larval, pupal, and adult stage
on _Solidago sempervirens_, one at Harpswell, Maine, the other at Woods
Hole, Massachusetts. The adult insects of the two species differ
slightly in size and color, the germ cells mainly in the number of
chromosomes, _Trirhabda virgata_ having 28 and _Trirhabda canadense_ 30
in spermatogonia and somatic cells.

In _Trirhabda virgata_, the metaphase of a spermatogonial mitosis (plate
VIII, fig. 3) contains 28 chromosomes, one of which, as in _Tenebrio
molitor_ is very much smaller than any of the others. The maternal
homologue of the small chromosome is, as later stages show, one of the
largest chromosomes. In _Tenebrio_ the unequal pair could not be
distinguished in the growth stages of the spermatocytes. In _Trirhabda_
it has not been detected in the synizesis stage (fig. 4), but in the
later growth stages (figs. 5-7) this pair is conspicuous in preparations
stained by the various methods cited above, while the spireme is pale
and inconspicuous. The size of the heterochromosome pair varies
considerably at different times in the growth period, and in some nuclei
(fig. 7) both chromosomes appear to be attached to a plasmosome. The
ordinary chromosomes assume the form of rings and crosses in the
prophase of the first maturation mitosis (fig. 8), but usually appear in
the spindle as dumb-bells or occasionally as tetrads (fig. 10), or
crosses (fig. 11). The unsymmetrical pair is plainly seen in figures 9
and 11, but is not distinguishable in a polar view of the metaphase
(fig. 13). In the anaphase (figs. 14-16) the larger and the smaller
components of the pair separate as in _Tenebrio_. This is, therefore,
clearly a reducing division as far as this pair is concerned, and
probably for all of the other pairs, though n