Such an experiment requires a considerable number of subjects, as the weak and maimed, who may be many, must be rejected. Chalicodoma muraria cannot furnish the quantity needed; it is not common enough, and I am anxious not to disturb the small people by the Aigues whom I want for other observations later. Fortunately I have near my house, under the projecting edge of the roof of a shed, a magnificent colony of Chalicodoma sicula in full activity. I can draw at pleasure on the populous city. The insect is small—less than half the size of C. muraria; no matter—all the more merit if it can traverse the four kilometres which I have in reserve for it, and find its nest. I took forty, isolating them as usual in paper cones. A ladder was placed against the wall in order to reach the nest; it was to be used by my daughter Aglaë, to allow her to mark the exact instant when the first one returned. I set the clock on the mantelpiece and my watch together, that I might compare the moment of departure and arrival. Then I carried off my forty captives to the spot where Chalicodoma muraria works beside the Aygues. The expedition had a double scope—to observe Réaumur’s mason bee and set the Sicilian one free. The latter would have to fly back four kilometres. At length my prisoners were released—all marked with a large white dot in the middle of the thorax. It is not for nothing that one successively handles forty wrathful Hymenoptera which forthwith unsheath and make play with their poisoned stings. Before the mark could be made, too often the stab was given, and my burning fingers moved in self-defence sometimes against my will; I handled them with more consideration for myself than for the insect, and sometimes squeezed my bees too hard. To experiment in order to lift a small corner of the veil that covers a truth is a beautiful and noble thing, which can enable one to brave many perils, yet surely one may show a little impatience if in a brief space of time one’s finger tips get stung forty times. If any one should reproach me for my clumsy handling, I would suggest that he make the experiment, and then judge how far the situation was pleasant. In short, either from the fatigue of the journey, or because I pressed too hard and injured some articulations, out of my forty Hymenoptera only twenty flew off strongly and unhesitatingly; the rest strayed over the herbage near at hand, unable to keep their balance, or remained on the willows where I had put them, refusing to fly even when excited by a straw. These faint-hearted ones, these maimed ones, these incapables hurt by my fingers, must be struck off the list. Twenty started with an unhesitating flight. That was amply sufficient.