erving-hatch, according to
the diameter. These mark out the first cells, one after the other, which
are reserved solely for the females. Then comes the last whorl, which
is much too wide for a single row of cells; and here we once more find,
exactly as in a wide reed, a costly profusion of masonry, an irregular
arrangement of the cells and a mixture of the sexes.

Having said so much, let us go back to the Osmia of the quarries. Why,
when I offer them simultaneously Snail-shells and reeds of a suitable
size, do the old frequenters of the shells prefer the reeds, which in
all probability have never before been utilized by their race? Most of
them scorn the ancestral dwelling and enthusiastically accept my reeds.
Some, it is true, take up their quarters in the Snail-shell; but even
among these a goodly number refuse my new shells and return to their
birth-place, the old Snail-shell, in order to utilize the family
property, without much labour, at the cost of a few repairs. Whence,
I ask, comes this general preference for the cylinder, never used
hitherto? The answer can be only this: of two lodgings at her disposal
the Osmia selects the one that provides a comfortable home at a minimum
outlay. She economizes her strength when restoring an old nest; she
economizes it when replacing the Snail-shell by the reed.

Can animal industry, like our own, obey the law of economy, the sovran
law that governs our industrial machine even as it governs, at least to
all appearances, the sublime machine of the universe? Let us go
deeper into the question and bring other workers into evidence, those
especially who, better equipped perhaps and at any rate better fitted
for hard work, attack the difficulties of their trade boldly and look
down upon alien establishments with scorn. Of this number are the
Chalicodomae, the Mason-bees proper.

The Mason-bee of the Pebbles does not make up her mind to build a
brand-new dome unless there be a dearth of old and not quite dilapidated
nests. The mothers, sisters apparently and heirs-at-law to the domain,
dispute fiercely for the ancestral abode. The first who, by sheer brute
force, takes possession of the dome, perches upon it and, for long
hours, watches events while polishing her wings. If some claimant puts
in an appearance, forthwith the other turns her out with a volley of
blows. In this way the old nests are employed so long as they have not
become uninhabitable hovels.

Without being equa