We will now open the nest of the balloon-building Wasp. Here is something that we did not expect. Instead of one envelope there are two, one enclosed within the other, with a slight interval between. There would have been even more, three or four of them, had not impatient hands, eager to bring me the masterpiece, culled it before it reached perfection. The nest is incomplete, as is proved by the single story of cells. A perfect Wasps’-nest would contain several stories. No matter: such as it is, this work shows us that the chilly Wasp was acquainted with the art of preserving heat before we were. Physics teaches us the efficacy of a cushion of air, motionless between two walls, as a preventive against cooling; it recommends the use of double windows to maintain a mild temperature in our houses in winter. Long before the days of human science, the little Wasp, that passionate lover of warmth, knew the secret of multiple envelopes containing layers of air. With its three or four balloons, fitting within one another, her nest, hanging in the sun, must turn into a vapour-bath. These paper containers are merely defensive works; the actual city, for which all the rest has been built, occupies the top of the dome. It consists at present of a single layer of hexagonal cells, open below. Later on, other, similar layers would have been added, descending in stages and each connected with its predecessor by little papier mâché columns. The aggregate of these layers, or combs, would supply not far short of a hundred cells, the lodgings of as many larvæ. The method of rearing imposes on the Social Wasps rules unknown to the other builders. These latter store in each cell provisions—honey or game—apportioned to the grub’s needs. The egg once laid, they close the cell. The rest does not concern them: the immured larva will find all around it the wherewithal to nourish itself and to thrive without outside help. Under these conditions, the irregular grouping of the cells is of trifling importance; disorder even is admissible, provided that the whole group be in a place of safety, if need be under the cover of a protective casing. Richly supplied with provender and tranquil in its crypt, none of the recluses expects anything from the outer world.