s if the insect did not first mark out its confines.
Can there really be an act of measuring? That would be superlatively
clever. Let us consult the Three-horned Osmia in her glass tubes.

The Osmia is working at her big partition, with her body outside the
cell which she is preparing. From time to time, with a pellet of mortar
in her mandibles, she goes in and touches the previous ceiling with
her forehead, while the tip of her abdomen quivers and feels the pad in
course of construction. One might well say that she is using the length
of her body as a measure, in order to fix the next ceiling at the
proper distance. Then she resumes her work. Perhaps the measure was
not correctly taken; perhaps her memory, a few seconds old, has already
become muddled. The Bee once more ceases laying her plaster and again
goes and touches the front wall with her forehead and the back wall with
the tip of her abdomen. Looking at that body trembling with eagerness,
extended to its full length to touch the two ends of the room, how can
we fail to grasp the architect's grave problem? The Osmia is measuring;
and her measure is her body. Has she quite done, this time? Oh dear
no! Ten times, twenty times, at every moment, for the least particle of
mortar which she lays, she repeats her mensuration, never being quite
certain that her trowel is going just where it should.

Meanwhile, amid these frequent interruptions, the work progresses and
the partition gains in width. The worker is bent into a hook, with her
mandibles on the inner surface of the wall and the tip of her abdomen
on the outer surface. The soft masonry stands between the two points of
purchase. The insect thus forms a sort of rolling-press, in which the
mud wall is flattened and shaped. The mandibles tap and furnish mortar;
the end of the abdomen also pats and gives brisk trowel-touches. This
anal extremity is a builder's tool; I see it facing the mandibles on
the other side of the partition, kneading and smoothing it all over,
flattening the little lump of clay. It is a singular implement, which
I should never have expected to see used for this purpose. It takes an
insect to conceive such an original idea, to do mason's work with its
behind! During this curious performance, the only function of the legs
is to keep the worker steady by spreading out and clinging to the walls
of the tunnel.

The partition with the hole in it is finished. Let us go back to the
measuring of which