orae are
the actual pioneers, the work of boring the galleries is wholly
theirs; and their cells are situated right at the end. The Osmia
profits by the galleries which have been abandoned either because of
their age, or because of the completion of the cells occupying the
most distant part; she builds her cells by dividing these corridors
into unequal and inartistic chambers by means of rude earthen
partitions. The Osmia's sole achievement in the way of masonry is
confined to these partitions. This, by the way, is the ordinary
building-method adopted by the various Osmiae, who content themselves
with a chink between two stones, an empty Snail-shell, or the dry and
hollow stem of some plant, wherein to build their stacks of cells, at
small expense, by means of light partitions of mortar.

[Footnote 4: Cf. _Bramble-bees and Others_: _passim_.--_Translator's
Note_.]

The cells of the Anthophora, with their faultless geometrical
regularity and their perfect finish, are works of art, excavated, at a
suitable depth, in the very substance of the loamy bank, without any
manufactured part save the thick lid that closes the orifice. Thus
protected by the prudent industry of their mother, well out of reach
in their distant, solid retreats, the Anthophora's larvae are devoid
of the glandular apparatus designed for secreting silk. They therefore
never spin a cocoon, but lie naked in their cells, whose inner surface
has the polish of stucco.

In the Osmia's cells, on the other hand, means of defence are
required, for these are situated in the surface layer of the bank;
they are irregular in form, rough inside and barely protected, by
their thin earthen partitions, against external enemies. The Osmia's
larvae, in fact, contrive to enclose themselves in an egg-shaped
cocoon, dark brown in colour and very strong, which preserves them
both from the rough contact of their shapeless cells and from the
mandibles of voracious parasites, Acari,[5] Cleri[6] and Anthreni,[7]
those manifold enemies whom we find prowling in the galleries, seeking
whom they may devour. It is by means of this equipoise between the
mother's talents and the larva's that the Osmia and the Anthophora, in
their early youth, escape some part of the dangers which threaten
them. It is easy therefore, in the bank excavated by these two Bees,
to recognize the property of either species by the situation and form
of the cells and also by their contents, which consist, wit