We must own that insect memory is a strange one, so lucid in general knowledge of locality, so limited as to its home. I should be disposed to name it topographical instinct; the creature knows the localities, but not the dear nest—the dwelling. The Bembex led us to a like conclusion. The nest being laid open, she cared nothing for the family—for the larva writhing distressfully in the sun unrecognised. What they do recognise, what they seek, and find with marvellous precision, is the place where no longer exists anything of the entrance door—not even a threshold. If any doubt remain as to the powerlessness of Chalicodoma muraria to know her nest except by the place which the pebble occupies on the ground, this may set it at rest. I substituted a nest of one mason bee for that of another, as alike as might be, both in masonry and storage. Of course this exchange and those of which I shall speak later were made during the absence of the owner. In the nest not hers, but placed where her own had been, she established herself without hesitation. If she had been building, I offered her a cell in process of construction, and she worked on with the same care and zeal as if the work already done had been her own. If she were bringing honey and pollen, I offered a cell partly stored. Her journeys continued, with honey in her crop and pollen underneath her body to complete filling the store of another bee. Thus the bee does not suspect the exchange, nor distinguish what is and is not hers. She thinks she is continuing to work at a cell really her own. After leaving her for a time in possession of the exchanged nest, I restored her own. The fresh change passed unobserved; her labour was continued in the cell restored to her, at the point at which it had arrived in the substituted one. Then I once more substituted the strange nest, and still she persisted in her labour. Thus alternating nests at the same spot, I thoroughly convinced myself that the insect cannot perceive the difference between that which is her own and that which is not. Whether the cell be hers or not, she works with equal fervour, provided that the basis for the edifice—the stone—remains in its original position. One may lend a livelier interest to the experiment by using two neighbouring nests—work at which is about equally advanced. I transpose them, placing one where the other was; the distance is hardly a cubit. Despite this close neighbourhood, which allows the bees to see both nests at once and choose between them, the two bees on arriving each immediately alighted on the substituted nest and went on working at it. We may change the two nests at pleasure; we shall still see the two mason bees keep to the spot chosen by them and work in turn—now at their own cell, now at that of the other.