I have observed the same thing in the nests of the Mason-bee of the Sheds, but not so easily. The series are shorter here, because the Mason-bee does not bore galleries but builds cell upon cell. The work of the whole swarm thus forms a stratum of cells that grows thicker from year to year. The corridors occupied by the Osmia are the holes which the Mason-bee dug in order to reach daylight from the deep layers. In these short series, both sexes are usually present; and, if the Mason-bee's chamber is at the end of the passage, it is inhabited by a female Osmia. We come back to what the short tubes and the old nests of the Mason-bee of the Pebbles have already taught us. The Osmia who, in tubes of sufficient length, divides her whole laying into a continuous sequence of females and a continuous sequence of males, now breaks it up into short series in which both sexes are present. She adapts her sectional layings to the exigencies of a chance lodging; she always places a female in the sumptuous chamber which the Mason-bee or the Anthophora occupied originally. Facts even more striking are supplied by the old nests of the Masked Anthophora (A. personata, ILLIG.), old nests which I have seen utilized by the Horned Osmia and the Three-horned Osmia at the same time. Less frequently, the same nests serve for Latreille's Osmia. Let us first describe the Masked Anthophora's nests. In a steep bank of sandy clay, we find a set of round, wide-open holes. There are generally only a few of them, each about half an inch in diameter. They are the entrance-doors leading to the Anthophora's abode, doors always left open, even after the building is finished. Each of them gives access to a short passage, sometimes straight, sometimes winding, nearly horizontal, polished with minute care and varnished with a sort of white glaze. It looks as if it had received a thin coat of whitewash. On the inner surface of this passage, in the thickness of the earthy bank, spacious oval niches have been excavated, communicating with the corridor by means of a narrow bottle-neck, which is closed, when the work is done, with a substantial mortar stopper. The Anthophora polishes the outside of this stopper so well, smooths its surface so perfectly, bringing it to the same level as that of the passage, is so careful to give it the white tint of the rest of the wall that, when the job is finished, it becomes absolutely impossible to distinguish the entrance-door corresponding with each cell.