zens of nests of both species. In at least half the cases, the two
sexes were present together; the female, the smaller, occupied the front
cell and the male, the bigger, the back cell. Other cells, which were
smaller or too much obstructed at the back by the dried-up remains of
the Mollusc, contained only one cell, occupied at one time by a female
and at another by a male. A few, lastly, had both cells inhabited now by
two males and now by two females. The most frequent arrangement was the
simultaneous presence of both sexes, with the female in front and the
male behind. The Anthidia who make resin-dough and live in Snail-shells
can therefore alternate the sexes regularly to meet the exigencies of
the spiral dwelling-house.

One more thing and I have done. My apparatus of reeds, fixed against the
walls of the garden, supplied me with a remarkable nest of the Horned
Osmia. The nest is established in a bit of reed 11 millimetres wide
inside. (.429 inch--Translator's Note.) It comprises thirteen cells and
occupies only half the cylinder, although the orifice is plugged with
the usual stopper. The laying therefore seems here to be complete.

Well, this laying is arranged in a most singular fashion. There is
first, at a suitable distance from the bottom or the node of the reed, a
transversal partition, perpendicular to the axis of the tube. This marks
off a cell of unusual size, in which a female is lodged. After that,
in view of the excessive width of the tunnel, which is too great for
a series in single file, the Osmia appears to alter her mind. She
therefore builds a partition perpendicular to the transversal partition
which she has just constructed and thus divides the second storey into
two rooms, a larger room, in which she lodges a female, and a smaller,
in which she lodges a male. She next builds a second transversal
partition and a second longitudinal partition perpendicular to it. These
once more give two unequal chambers, stocked likewise, the large one
with a female, the smaller one with a male.

From this third storey onwards, the Osmia abandons geometrical
accuracy; the architect seems to be a little out in her reckoning. The
transversal partitions become more and more slanting and the work
grows irregular, but always with a sprinkling of large chambers for the
females and small chambers for the males. Three females and two males
are housed in this way, the sexes alternating.

By the time that the base of t