It may happen that the Osmia's patience is in vain and that the barricade that blocks the way never disappears at all. Sometimes, the egg in a cell does not mature; and the unconsumed provisions dry up and become a compact, sticky, mildewed plug, through which the occupants of the floors below could never clear themselves a passage. 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 placed together and fastened. A little putty does away with the joint and prevents the least ray of light from penetrating. Lastly, the apparatus is hung up perpendicularly, with the cocoons' heads up. We have now only to wait. None of the Osmiae can get out in the usual manner, because each of them is confined between two partitions coated with sealing-wax. There is but one resource left to them if they would emerge into the light of day, that is, for each of them to open a side-window, provided always that they possess the instinct and the power to do so.