he eleventh cell is reached, the
transversal partition is once more almost perpendicular to the axis.
Here what happened at the bottom is repeated. There is no longitudinal
partition; and the spacious cell, covering the whole diameter of the
cylinder, receives a female. The edifice ends with two transversal
partitions and one longitudinal partition, which mark out, on the same
level, chambers twelve and thirteen, both of which contain males.

There is nothing more curious than this mixing of the two sexes, when
we know with what precision the Osmia separates them in a linear series,
where the narrow width of the cylinder demands that the cells shall be
set singly, one above the other. Here, the Bee is making use of a tube
whose diameter is not suited to her work; she is constructing a complex
and difficult edifice, which perhaps would not possess the necessary
solidity if the ceilings were too broad. The Osmia therefore supports
these ceilings with longitudinal partitions; and the unequal chambers
resulting from the introduction of these partitions receive females at
one time and males at another, according to their capacity.

CHAPTER 5. PERMUTATIONS OF SEX.

The sex of the egg is optional. The choice rests with the mother, who is
guided by considerations of space and, according to the accommodation
at her disposal, which is frequently fortuitous and incapable of
modification, places a female in this cell and a male in that, so that
both may have a dwelling of a size suited to their unequal development.
This is the unimpeachable evidence of the numerous and varied facts
which I have set forth. People unfamiliar with insect anatomy--the
public for whom I write--would probably give the following explanation
of this marvellous prerogative of the Bee: the mother has at her
disposal a certain number of eggs, some of which are irrevocably female
and the others irrevocably male: she is able to pick out of either group
the one which she wants at the actual moment; and her choice is decided
by the holding capacity of the cell that has to be stocked. Everything
would then be limited to a judicious selection from the heap of eggs.

Should this idea occur to him, the reader must hasten to reject it.
Nothing could be more false, as the merest reference to anatomy will
show. The female reproductive apparatus of the Hymenoptera consists
generally of six ovarian tubes, something like glove-fingers, divided
into bunches of thre