uantities of
provisions. The real females, the Queen-bees, have wax cells
incomparably more spacious than the cells of the males and receive a
much larger amount of food. Everything therefore demonstrates that we
are here in the presence of a general rule.

OPTIONAL DETERMINATION OF THE SEXES.

But does this rule express the whole truth? Is there nothing beyond a
laying in two series? Are the Osmiae, the Chalicodomae and the rest of
them fatally bound by this distribution of the sexes into two distinct
groups, the male group following upon the female group, without any
mixing of the two? Is the mother absolutely powerless to make a change
in this arrangement, should circumstances require it?

The Three-pronged Osmia already shows us that the problem is far from
being solved. In the same bramble-stump, the two sexes occur very
irregularly, as though at random. Why this mixture in the series of
cocoons of a Bee closely related to the Horned Osmia and the
Three-horned Osmia, who stack theirs methodically by separate sexes in
the hollow of a reed? What the Bee of the brambles does cannot her
kinswomen of the reeds do too? Nothing, so far as I know, explains this
fundamental difference in a physiological act of primary importance.
The three Bees belong to the same genus; they resemble one another in
general outline, internal structure and habits; and, with this close
similarity, we suddenly find a strange dissimilarity.

There is just one thing that might possibly arouse a suspicion of the
cause of this irregularity in the Three-pronged Osmia's laying. If I
open a bramble-stump in the winter to examine the Osmia's nest, I find
it impossible, in the vast majority of cases, to distinguish positively
between a female and a male cocoon: the difference in size is so small.
The cells, moreover, have the same capacity: the diameter of the
cylinder is the same throughout and the partitions are almost always
the same distance apart. If I open it in July, the victualling-period,
it is impossible for me to distinguish between the provisions destined
for the males and those destined for the females. The measurement of
the column of honey gives practically the same depth in all the cells.
We find an equal quantity of space and food for both sexes.

This result makes us foresee what a direct examination of the two sexes
in the adult form tells us. The male does not differ materially from
the female in respect of size. If he is a trif