Sometimes, again, a grub dies in its cocoon; and the cradle of the
deceased, now turned into a coffin, forms an everlasting obstacle.
How shall the insect cope with such grave circumstances?

Among the many bramble-stumps which I have collected, some few have
presented a remarkable peculiarity. In addition to the orifice at the
top, they had at the side one and sometimes two round apertures that
looked as though they had been punched out with an instrument. On
opening these stalks, which were old, deserted nests, I discovered
the cause of these very exceptional windows. Above each of them was a
cell full of mouldy honey. The egg had perished and the provisions
remained untouched: hence the impossibility of getting out by the
ordinary road. Walled in by the unsurmountable obstacle, the Osmia on
the floor below had contrived an outlet through the side of the
shaft; and those in the lower storeys had benefited by this ingenious
innovation. The usual door being inaccessible, a side-window had been
opened by means of the insect's jaws. The cocoons, torn, but still in
position in the lower rooms, left no doubt as to this eccentric mode
of exit. The same fact, moreover, was repeated, in several bramble-
stumps, in the case of Osmia tridentata; it was likewise repeated in
the case of Anthidium scapulare. The observation was worth confirming
by experiment.

I select a bramble-stem with the thinnest rind possible, so as to
facilitate the Osmiae's work. I split it in half, thus obtaining a
smooth-sided trough which will enable me to judge better of future
exits. The cocoons are next laid out in one of the troughs. I
separate them with disks of sorghum, covering both surfaces of the
disk with a generous layer of sealing-wax, a material which the
Osmia's mandibles are not able to attack. The two troughs are then