call for them. They are placed horizontally, or nearly so, side by
side, with no attempt at orderly arrangement. Each architect has
plenty of elbow-room and builds as and where she pleases, on the one
condition that she does not hamper her neighbours' work; otherwise she
can look out for rough handling from the parties interested. The
cells, therefore, accumulate at random in this workyard where there is
no organization. Their shape is that of a thimble divided down the
middle; and their walls are completed either by the adjoining cells or
by the surface of the old nest. Outside, they are rough and display
successive layers of knotted cords corresponding with the different
courses of mortar. Inside, the walls are flat without being smooth;
later on, the grub's cocoon will make up for any lack of polish.

Each cell, as built, is stocked and walled up immediately, as we have
seen with the Mason-bee of the Walls. This work goes on throughout the
best part of May. All the eggs are laid at last; and then the Bees,
without drawing distinctions between what does and what does not
belong to them, set to work in common on a general protection for the
colony. This is a thick coat of mortar, which fills up the gaps and
covers all the cells. In the end, the common nest presents the
appearance of a wide expanse of dry mud, with very irregular
protuberances, thicker in the middle, the original nucleus of the
establishment, thinner at the edges, where as yet there are only newly
built cells, and varying greatly in dimensions according to the number
of workers and therefore to the age of the nest first founded. Some of
these nests are hardly larger than one's hand, while others occupy the
greater part of the projecting edge of a roof and are measured by
square yards.

When working alone, which is not unusual, on the shutter of a disused