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.

Some of them were occupied on the first few days of the laying; and the Osmia who had started with a home of this sort would pass next to a second Snail-shell, in the immediate neighbourhood of the first, to a third, a fourth and others still, always close together, until her ovaries were emptied.

The whole family of one mother would thus be lodged in Snail-shells which were duly marked with the date of the laying and a description of the worker.