icted to the Three-horned Osmia; it is also
frequently found in the case of the Horned Osmia and of Latreille's
Osmia. Nothing could be prettier than the work of the last-named, who
goes to the plants for her material and fashions a delicate sheet in
which she cuts a graceful arch. The Chinaman partitions his house with
paper screens; Latreille's Osmia divides hers with disks of thin green
cardboard perforated with a serving-hatch which remains until the room
is completely furnished. When we have no glass houses at our disposal,
we can see these little architectural refinements in the reeds of the
hurdles, if we open them at the right season.

By splitting the bramble-stumps in the course of July, we perceive also
that the Three-pronged Osmia notwithstanding her narrow gallery,
follows the same practice as Latreille's Osmia, with a difference. She
does not build a party-wall, which the diameter of the cylinder would
not permit; she confines herself to putting up a frail circular pad of
green putty, as though to limit, before any attempt at harvesting, the
space to be occupied by the Bee-bread, whose depth could not be
calculated afterwards if the insect did not first mark out its
confines.

If, in order to see the Osmia's nest as a whole, we split a reed
lengthwise, taking care not to disturb its contents; or, better still,
if we select for examination the string of cells built in a glass tube,
we are forthwith struck by one detail, namely, the uneven distances
between the partitions, which are placed almost at right angles to the
axis of the cylinder. It is these distances which fix the size of the
chambers, which, with a similar base, have different heights and
consequently unequal holding-capacities. The bottom partitions, the
oldest, are farther apart; those of the front part, near the orifice,
are closer together. Moreover, the provisions are plentiful in the
loftier cells, whereas they are niggardly and reduced to one-half or
even one-third in the cells of lesser height. Let me say at once that
the large cells are destined for the females and the small ones for the
males.

DISTRIBUTION OF THE SEXES.

Does the insect which stores up provisions proportionate to the needs
of the egg which it is about to lay know beforehand the sex of that
egg? Or is the truth even more paradoxical? What we have to do is to
turn this suspicion into a certainty demonstrated by experiment. And
first let us find out how the sexes ar