he 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
window, on a stone, or on a twig in some hedge, the Sicilian Chalicodoma
behaves in just the same way. For instance, should she settle on a twig,
the Bee begins by solidly cementing the base of her cell to the slight
foundation. Next, the building rises, taking the form of a little
upright turret. This first cell, when victualled and sealed, is followed
by another, having as its support, in addition to the twig, the cells
already built. From six to ten chambers are thus grouped side by side.
Lastly, one coat of mortar covers everything, including the twig itself,
which provides a firm mainstay for the whole.

CHAPTER 2. EXPERIMENTS.

As the nests of the Mason-bee of the Walls are erected on small-sized
pebbles, which can be easily carried wherever you like and moved about
from one place to another, without disturbing either the work of
the builder or the repose of the occupants of the cells, they lend
themselves readily to practical experiment, the only method that can
throw a little light on the nature of instinct. To study the insect's
mental faculties to any purpose, it is not enough for the observer to be
able to profit by some ha