she is going to
lay, because that egg is placed in a cell of the proper capacity. We
can go further, and admit that the mother alters the order of
succession of the sexes at her pleasure, because her layings, between
one old nest and another, are broken up into small groups of males and
females according to the exigencies of space in the actual nest which
she happens to be occupying.

Here then is the Chalicodoma, when mistress of an old nest of which she
has not the power to alter the arrangement, breaking up her laying into
sections comprising both sexes just as required by the conditions
imposed upon her. She therefore decides the sex of the egg at will,
for, without this prerogative, she could not, in the chambers of the
nest which she owes to chance, deposit unerringly the sex for which
those chambers were originally built; and this happens however small
the number of chambers to be filled.

When the mother herself founds the dwelling, when she lays the first
rows of bricks, the females come first and the males at the finish.
But, when she is in the presence of an old nest, of which she is quite
unable to alter the general arrangement, how is she to make use of a
few vacant rooms, the large and small alike, if the sex of the egg be
already irrevocably fixed? She can only do so by abandoning the
arrangement in two consecutive rows and accommodating her laying to the
varied exigencies of the home. Either she finds it impossible to make
an economical use of the old nest, a theory refuted by the evidence, or
else she determines at will the sex of the egg which she is about to
lay.

The Osmiae themselves will furnish the most conclusive evidence on the
latter point. We have seen that these Bees are not generally miners,
who themselves dig out the foundation of their cells. They make use of
the old structures of others, or else of natural retreats, such as
hollow stems, the spirals of empty shells and various hiding-places in
walls, clay or wood. Their work is confined to repairs to the house,
such as partitions and covers. There are plenty of these retreats; and
the insects would always find first-class ones if it thought of going
any distance to look for them. But the Osmia is a stay-at-home: she
returns to her birthplace and clings to it with a patience extremely
difficult to exhaust. It is here, in this little familiar corner, that
she prefers to settle her progeny. But then the apartments are few in
number and