made by a dab of clay placed at right angles to the
axis of the cylinder, at a distance from the bottom determined by the
ordinary length of a cell. This wad is not a complete round; it is more
crescent-shaped, leaving a circular space between it and one side of the
tube. Fresh layers are swiftly added to the dab of clay; and soon the
tube is divided by a partition which has a circular opening at the side
of it, a sort of dog-hole through which the Osmia will proceed to knead
the Bee-bread. When the victualling is finished and the egg laid upon
the heap, the hole is closed and the filled-up partition becomes the
bottom of the next cell. Then the same method is repeated, that is to
say, in front of the just completed ceiling a second partition is built,
again with a side-passage, which is stouter, owing to its distance from
the centre, and better able to withstand the numerous comings and goings
of the housewife than a central orifice, deprived of the direct support
of the wall, could hope to be. When this partition is ready, the
provisioning of the second cell is effected; and so on until the wide
cylinder is completely stocked.

The building of this preliminary party-wall, with a narrow, round
dog-hole, for a chamber to which the victuals will not be brought until
later is not restricted 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 afterward