dle, the female
occupying the lower and the male the upper storey. True, in such cases
economy of space is strained to the utmost, the apartments provided by
the Mason-bee of the Shrubs being very small as it is, despite their
entrance-halls. Lastly, the deeper cavities on the circumference are
allotted to females and the shallower to males.

I will add that a single mother peoples each nest and also that she
proceeds from cell to cell without troubling to ascertain the depth. She
goes from the centre to the edges, from the edges to the centre, from a
deep cavity to a shallow cavity and vice versa, which she would not
do if the sexes were to follow upon each other in a settled order. For
greater certainty, I numbered the cells of one nest as each of them was
closed. On opening them later, I was able to see that the sexes were
not subjected to a chronological arrangement. Females were succeeded by
males and these by females without its being possible for me to make out
any regular sequence. Only--and this is the essential point--the deep
cavities were allotted to the females and the shallow ones to the males.

We know that the Three-horned Osmia prefers to haunt the habitations of
the Bees who nidify in populous colonies, such as the Mason-bee of the
Sheds and the Hairy-footed Anthophora. Exercising the very greatest
care, I broke up some great lumps of earth removed from the banks
inhabited by the Anthophora and sent to me from Carpentras by my dear
friend and pupil M. Devillario. I examined them conscientiously in the
quiet of my study. I found the Osmia's cocoons arranged in short series,
in very irregular passages, the original work of which is due to the
Anthophora. Touched up afterwards, made larger or smaller, lengthened
or shortened, intersected with a network of crossings by the numerous
generations that had succeeded one another in the same city, they formed
an inextricable labyrinth.

Sometimes these corridors did not communicate with any adjoining
apartment; sometimes they gave access to the spacious chamber of the
Anthophora, which could be recognized, in spite of its age, by its oval
shape and its coating of glazed stucco. In the latter case, the bottom
cell, which once constituted, by itself, the chamber of the Anthophora,
was always occupied by a female Osmia. Beyond it, in the narrow
corridor, a male was lodged, not seldom two, or even three. Of course,
clay partitions, the work of the Osmia, separated