The account which Réaumur has given of the operations of this class of bees differs considerably from that which we have here detailed; from the species being different, or from his bees not having been able to procure moist clay. On the contrary, sand was the chief material used by the mason-bees (_Megachile muraria_); which they had the patience to select from the walks of a garden, and knead into a paste or mortar, adapted to their building. They had consequently to expend a much greater quantity of saliva than our bees (_Osmia bicornis_), which worked with moist clay. Réaumur, indeed, ascertained that every individual grain of sand is moistened previous to its being joined to the pellet, in order to make it adhere more effectually. The tenacity of the mass is, besides, rendered stronger, he tells us, by adding a proportion of earth or garden-mould. In this manner, a ball of mortar is formed, about the size of a small shot, and carried off to the nest. When the structure of this is examined, it has all the appearance externally of being composed of earth and small stones or gravel. The ancients, who were by no means accurate naturalists, having observed bees carrying pellets of earth and small stones, supposed that they employed these to add to their weight, in order to steady their flight when impeded by the wind. The nests thus constructed appear to have been more durable edifices than those which have fallen under our observation;--for Réaumur says they were harder than many sorts of stone, and could scarcely be penetrated with a knife. Ours, on the contrary, do not seem harder than a piece of sun-baked clay, and by no means so hard as brick. One circumstance appeared inexplicable to Réaumur and his friend Du Hamel, who studied the operations of these insects in concert. After taking a portion of sand from one part of the garden-walk, the bees usually took another portion from a spot almost twenty and sometimes a hundred paces off, though the sand, so far as could be judged by close examination, was precisely the same in the two places. We should be disposed to refer this more to the restless character of the insect than to any difference in the sand. We have observed a wasp paring the outside of a plank, for materials to form its nest; and though the plank was as uniform in the qualities of its surface, nay, probably more so than the sand could be, the wasp fidgeted about, nibbling a fibre from one, and a fibre from another portion, till enough was procured for one load. In the same way, the whole tribe of wasps and bees flit restlessly from flower to flower, not unfrequently revisiting the same blossom, again and again, within a few seconds. It appears to us, indeed, to be far from improbable, that this very restlessness and irritability may be one of the springs of their unceasing industry.