en nothing at her disposal except the cell proper, a spacious
apartment in which one of the Osmia's females will find ample
accommodation, for she is much smaller than the original occupant of the
chamber, no matter the sex; but there is not room for two cocoons at
a time, especially in view of the space taken up by the intervening
partition. Well, in those large, well-built chambers, formerly the homes
of Chalicodomae, the Osmia settles females and none but females.

Let us now consider the long vestibule. Here, a partition is
constructed, encroaching slightly on the cell proper, and the residence
is divided into two unequal storeys, a large room below, housing a
female, and a narrow cabin above, containing a male.

When the length of the vestibule permits, allowing for the space
required by the outer stopper, a third storey is built, smaller than the
second; and another male is lodged in this cramped corner. In this way
the old nest of the Mason-bee of the Pebbles is colonized, cell after
cell, by a single mother.

The Osmia, as we see, is very frugal of the lodging that has fallen to
her share; she makes the best possible use of it, giving to the females
the spacious chambers of the Mason-bee and to the males the narrow
vestibules, subdivided into storeys when this is feasible. Economy of
space is the chief consideration, since her stay-at-home tastes do not
allow her to indulge in distant quests. She has to employ the site which
chance places at her disposal just as it is, now for a male and now for
a female. Here we see displayed, more clearly than ever, her power of
deciding the sex of the egg, in order to adapt it judiciously to the
conditions of the house-room available.

I had offered at the same time to the Osmiae in my study some old
nests of the Mason-bee of the Shrubs, which are clay spheroids with
cylindrical cavities in them. These cavities are formed, as in the old
nests of the Mason-bee of the Pebbles, of the cell properly so-called
and of the exit-way which the perfect insect cut through the outer
coating at the time of its deliverance. Their diameter is about seven
millimetres (.273 inch.--Translator's Note.); their depth at the centre
of the heap is 23 millimetres (.897 inch.--Translator's Note.); and at
the edge averages 14 millimetres (.546 inch.--Translator's Note.)

The deep central cells receive only the females of the Osmia; sometimes
even the two sexes together, with a partition in the mid