ferences:
one with its eight empty chambers and its spreading clay dome; the other
with its single bare cell, at most the size of an acorn.

Well, the two Mason-bees do not hesitate long in front of these
exchanged nests, not three feet away from each other. Each makes for the
site of her late home. One, the original owner of the old nest, finds
nothing but a solitary cell. She rapidly inspects the pebble and,
without further formalities, first plunges her head into the strange
cell, to disgorge honey, and then her abdomen, to deposit pollen. And
this is not an action due to the imperative need of ridding herself as
quickly as possible, no matter where, of an irksome load, for the Bee
flies off and soon comes back again with a fresh supply of provender,
which she stores away carefully. This carrying of provisions to
another's larder is repeated as often as I permit it. The other Bee,
finding instead of her one cell a roomy structure consisting of eight
apartments, is at first not a little embarrassed. Which of the eight
cells is the right one? In which is the heap of paste on which she had
begun? The Bee therefore visits the chambers one by one, dives right
down to the bottom and ends by finding what she seeks, that is to say,
what was in her nest when she started on her last journey, the nucleus
of a store of food. Thenceforward she behaves like her neighbour and
goes on carrying honey and pollen to the warehouse which is not of her
constructing.

Restore the nests to their original places, exchange them yet once
again and both Bees, after a short hesitation which the great difference
between the two nests is enough to explain, will pursue the work in the
cell of her own making and in the strange cell alternately. At last the
egg is laid and the sanctuary closed, no matter what nest happens to be
occupied at the moment when the provisioning reaches completion. These
incidents are sufficient to show why I hesitate to give the name of
memory to the singular faculty that brings the insect back to her nest
with such unerring precision and yet does not allow her to distinguish
her work from some one else's, however great the difference may be.

We will now experiment with Chalicodoma muraria from another
psychological point of view. Here is a Mason-bee building; she is at
work on the first course of her cell. I give her in exchange a cell not
only finished as a structure, but also filled nearly to the top with
honey. I h