Built on small pebbles which one can carry whither one will, remove, or interchange, without disturbing either the work of the constructor or the quiet of the inhabitants of the cells, the nests of Chalicodoma muraria lend themselves readily to experiment—the only method capable of throwing a little light on the nature of instinct. Profitably to study the physical faculties of the animal it is not enough to know how to turn to account such circumstances as a happy chance may offer to the observer: one must be capable of originating others, and vary them as much as possible and submit them to mutual control; in short, to give science a solid basis of fact one must experiment. Then some day will vanish before the evidence of exact documents the fantastic legends which cumber our books, such as the Scarabæus inviting his comrades to help in dragging his ball out of a rut, or a Sphex cutting up a fly to carry it in spite of the wind, and much more which is misused by those who desire to see in the animal world that which is not there. Thus, too, will materials be prepared which, used sooner or later by a learned hand, will cast premature and baseless theories back into oblivion. Réaumur generally confines himself to stating facts as they offered themselves to him in the normal course of things, and does not attempt to penetrate further into the powers of the insect by means of conditions brought about artificially. In his day there was everything to do, and the harvest was so great that the illustrious reaper hurried on to what was most urgent,—the gathering of it in, leading his successors to examine grain and ear in detail. Nevertheless, he mentions an experiment made on Chalicodoma muraria by his friend Du Hamel. The nest was placed in a glass funnel, the mouth of which was closed by a piece of gauze. Three males were hatched, which, though they had penetrated mortar hard as a stone, either did not attempt to pierce the thin gauze, or thought it beyond their power to do so. All three died under the glass. Insects generally only know how to execute that which they need to do in the common order of nature, adds Réaumur.