which she began her laying and go in search of another whereon to
deposit the rest of her eggs. She is too thrifty of her time and of her
mortar to involve herself in such expenditure except for grave reasons.
Consequently, each nest, at least when it is new, when the Bee herself
has laid the first foundations, contains the entire laying. It is a
different thing when an old nest is restored and made into a place for
depositing the eggs. I shall come back later to such houses.

A newly-built nest then, with rare exceptions, contains the entire
laying of one female. Count the cells and we shall have the total list
of the family. Their maximum number fluctuates round about fifteen.
The most luxuriant series will occasionally reach as many as eighteen,
though these are very scarce.

When the surface of the stone is regular all around the site of the
first cell, when the mason can add to her building with the same
facility in every direction, it is obvious that the groups of cells,
when finished, will have the oldest in the central portion and the more
recent in the surrounding portion. Because of this juxtaposition of
the cells, which serve partly as a wall to those which come next, it is
possible to form some estimate of the chronological order of the cells
in the Chalicodoma's nest and thus to discover the sequence of the two
sexes.

In winter, by which time the Bee has long been in the perfect state, I
collect Chalicodoma-nests, removing them bodily from their support with
a few smart sideward taps of the hammer on the pebbles. At the base of
the mortar dome the cells are wide agape and display their contents. I
take the cocoon from its box, open it and take note of the sex of the
insect enclosed.

I should probably be accused of exaggeration if I mentioned the total
number of the nests which I have gathered and the cells which I have
inspected by this method during the last six or seven years. I will
content myself with saying that the harvest of a single morning
sometimes consisted of as many as sixty nests of the Mason-bee. I had to
have help in carrying home my spoils, even though the nests were removed
from their stones on the spot.

From the enormous number of nests which I have examined, I am able to
state that, when the cluster is regular, the female cells occupy the
centre and the male cells the edges. Where the irregularity of the
pebble has prevented an even distribution around the initial point, the
sam