r laying lasted. He would indeed be
difficult to please who refused to bow before the results of these two
experiments. If, however, he is not yet convinced, here is something to
remove his last doubts.

The Three-horned Osmia often settles her family in old shells,
especially those of the Common Snail (Helix aspersa), who is so common
under the stone-heaps and in the crevices of the little unmortared
walls that support our terraces. In this species the spiral is wide
open, so that the Osmia, penetrating as far down as the helical passage
permits, finds, immediately above the point which is too narrow to
pass, the space necessary for the cell of a female. This cell is
succeeded by others, wider still, always for females, arranged in a
line in the same way as in a straight tube. In the last whorl of the
spiral, the diameter would be too great for a single row. Then
longitudinal partitions are added to the transverse partitions, the
whole resulting in cells of unequal dimensions in which males
predominate, mixed with a few females in the lower storeys. The
sequence of the sexes is therefore what it would be in a straight tube
and especially in a tube with a wide bore, where the partitioning is
complicated by subdivisions on the same level. A single Snail-shell
contains room for six or eight cells. A large, rough earthen stopper
finishes the nest at the entrance to the shell.

As a dwelling of this sort could show us nothing new, I chose for my
swarm the Garden Snail (Helix caespitum), whose shell, shaped like a
small swollen Ammonite, widens by slow degrees, the diameter of the
usable portion, right up to the mouth, being hardly greater than that
required by a male Osmia-cocoon. Moreover, the widest part, in which a
female might find room, has to receive a thick stopping-plug, below
which there will often be a free space. Under all these conditions, the
house will hardly suit any but males arranged one after the other.

The collection of shells placed at the foot of each hive includes
specimens of different sizes. The smallest are 18 millimetres (.7
inch.--Translator's Note.) in diameter and the largest 24 millimetres.
(.936 inch.--Translator's Note.) There is room for two cocoons, or
three at most, according to their dimensions.

Now these shells were used by my visitors without any hesitation,
perhaps even with more eagerness than the glass tubes, whose slippery
sides might easily be a little annoying to the Bee. So