in shape according to the supporting base. When set on a horizontal
surface, it rises like a little oval tower; when fixed against an
upright or slanting surface, it resembles the half of a thimble divided
from top to bottom. In this case, the support itself, the pebble,
completes the outer wall.

When the cell is finished, the Bee at once sets to work to victual it.
The flowers round about, especially those of the yellow broom (Genista
scoparia), which in May deck the pebbly borders of the mountain streams
with gold, supply her with sugary liquid and pollen. She comes with her
crop swollen with honey and her belly yellowed underneath with pollen
dust. She dives head first into the cell; and for a few moments you see
some spasmodic jerks which show that she is disgorging the honey-syrup.
After emptying her crop, she comes out of the cell, only to go in again
at once, but this time backwards. The Bee now brushes the lower side
of her abdomen with her two hind-legs and rids herself of her load of
pollen. Once more she comes out and once more goes in head first. It is
a question of stirring the materials, with her mandibles for a spoon,
and making the whole into a homogeneous mixture. This mixing-operation
is not repeated after every journey: it takes place only at long
intervals, when a considerable quantity of material has been
accumulated.

The victualling is complete when the cell is half full. An egg must now
be laid on the top of the paste and the house must be closed. All this
is done without delay. The cover consists of a lid of pure mortar, which
the Bee builds by degrees, working from the circumference to the centre.
Two days at most appeared to me to be enough for everything, provided
that no bad weather--rain or merely clouds--came to interrupt
the labour. Then a second cell is built, backing on the first and
provisioned in the same manner. A third, a fourth, and so on follow,
each supplied with honey and an egg and closed before the foundations
of the next are laid. Each task begun is continued until it is quite
finished; the Bee never commences a new cell until the four processes
needed for the construction of its predecessor are completed: the
building, the victualling, the laying of the egg and the closing of the
cell.

As the Mason-bee of the Walls always works by herself on the pebble
which she has chosen and even shows herself very jealous of her site
when her neighbours alight upon it, the number o