mark a plentiful number of my guests with a variety of dots on the
thorax, which enables me to follow any one Osmia from the beginning to
the end of her laying. The tubes and their respective holes are
numbered; a list, always lying open on my desk, enables me to note from
day to day, sometimes from hour to hour, what happens in each tube and
particularly the actions of the Osmiae whose backs bear distinguishing
marks. As soon as one tube is filled, I replace it by another.
Moreover, I have scattered in front of either hive a few handfuls of
empty Snail-shells, specially chosen for the object which I have in
view. Reasons which I will explain later led me to prefer the shells of
Helix caespitum. Each of the shells, as and when stocked, received the
date of the laying and the alphabetical sign corresponding with the
Osmia to whom it belonged. In this way, I spent five or six weeks in
continual observation. To succeed in an enquiry, the first and foremost
condition is patience. This condition I fulfilled; and it was rewarded
with the success which I was justified in expecting.

The tubes employed are of two kinds. The first, which are cylindrical
and of the same width throughout, will be of use for confirming the
facts observed in the first year of my experiments in indoor rearing.
The others, the majority, consist of two cylinders which are of very
different diameters, set end to end. The front cylinder, the one which
projects a little way outside the hive and forms the entrance-hole,
varies in width between 8 and 12 millimetres. (Between .312 and .468
inch.--Translator's Note.) The second, the back one, contained entirely
within my packing-case, is closed at its far end and is 5 to 6
millimetres in diameter. (.195 to .234 inch.--Translator's Note.) Each
of the two parts of the double-galleried tunnel, one narrow and one
wide, measures at most a decimetre in length. (3.9
inches.--Translator's Note.) I thought it advisable to have these short
tubes, as the Osmia is thus compelled to select different lodgings,
each of them being insufficient in itself to accommodate the total
laying. In this way I shall obtain a greater variety in the
distribution of the sexes. Lastly, at the mouth of each tube, which
projects slightly outside the case, there is a little paper tongue,
forming a sort of perch on which the Osmia alights on her arrival and
giving easy access to the house. With these facilities, the swarm
colonized fifty-two d