ature is still uncertain. The same green paste serves for the thick
plug that closes the abode. But in this case the insect does not use it
unadulterated. To give greater power of resistance to the work, it mixes
a number of bits of gravel with the vegetable cement. These materials,
which are easily picked up, are lavishly employed, as though the mother
feared lest she should not fortify sufficiently the entrance to her
dwelling. They form a sort of coarse stucco, on the more or less smooth
cupola of the Chalicodoma; and this unevenness, as well as the green
colouring of its mortar of masticated leaves, at once betrays the
Osmia's nest. In course of time, under the prolonged action of the air,
the vegetable putty turns brown and assumes a dead-leaf tint, especially
on the outside of the plug; and it would then be difficult for any one
who had not seen them when freshly made to recognize their nature.

The old nests on the pebbles seem to suit other Osmiae. My notes
mention Osmia Morawitzi, PEREZ, and Osmia cyanea, KIRB., as having been
recognized in these dwellings, although they are not very assiduous
visitors. Lastly, to complete the enumeration of the Bees known to me
as making their homes in the Mason's cupolas, I must add Megachile
apicalis, who piles in each cell a half-dozen or more honey-pots
constructed with disks cut from the leaves of the wild rose, and an
Anthidium whose species I cannot state, having seen nothing of her but
her white cotton sacks.

The Mason-bee of the Sheds, on the other hand, supplies free lodgings
to two species of Osmiae, Osmia tricornis, LATR., and Osmia Latreillii,
SPIN., both of whom are quite common. The Three-horned Osmia frequents
by preference the habitations of the Bees that build their nests
in populous colonies, such as the Chalicodoma of the Sheds and the
Hairy-footed Anthophora. Latreille's Osmia is nearly always found with
the Three-horned Osmia at the Chalicodoma's.

The real builder of the city and the exploiter of the labour of others
work together, at the same period, form a common swarm and live in
perfect harmony, each Bee of the two species attending to her business
in peace. They share and share alike, as though by tacit agreement. Is
the Osmia discreet enough not to put upon the good-natured Mason and
to utilize only abandoned passages and waste cells? Or does she take
possession of the home of which the real owners could themselves have
made use? I lean in favou