This is all done without delay. The orifice is closed by a cover of undiluted mortar, worked from the circumference to the centre. Two days, at most, seem required for the whole work.”[86] Afterwards several more cells—making a continuous group of from six to ten—are added, and when all is completed, the mason bee “builds a thick cover over the whole group, which, being of a material impermeable to water, and almost a non-conductor, is at once a defence against heat and cold and damp. This material is the usual mortar, made of earth and saliva, only with no small stones in it. The nest is now a rude dome, about as big as half an orange; one would take it for a clod of mud flung against a stone, where it had dried. Nothing outside betrays its contents—no suggestion of cells, none of labour. To the ordinary eye it is only a chance splash of mud.” Of course, when the eggs are hatched, the bee larvæ feed on the stored pollen and honey, a pleasing picture which suggests another something like it, though not altogether the same. I allude to certain species of solitary wasps, which, urged by the same feelings of maternal solicitude, choose a living caterpillar, grasshopper, spider, etc., for the future sustenance of their young. Take, for instance, _Ammophila urnaria_ of North America, whose habits in this respect have been carefully studied. This wasp is about an inch long, with very long legs, and a waist even exaggeratedly wasp-like. It is black in colour, but with a red mark running round the fore part of the abdomen. At the proper time she—for, of course, we are dealing with the female—may be seen running about the ground, and eagerly searching the various plants and grasses that come in her way. Occasionally, as though in lightness both of heart and body, she gives a leap off the ground, and at other times will fly up from it more deliberately, to make an examination of some overhanging leaf. At last, as a result of these little aerial excursions, let us say, she knocks down a certain green caterpillar of the kind wanted, and with maternal devotion full upon her, at once sets to work. The caterpillar, however, though taken by surprise, and assaulted the instant it has touched the ground, resists strenuously, as though instinctively knowing, and highly disapproving of, the fate in store for it. It is larger and more bulky than the wasp, and its contortions are so powerful that the latter is several times repulsed in her assaults. She is not discouraged, however, but continues perseveringly to fly at the caterpillar, till at last she takes it at a disadvantage, possibly in a moment of weariness, and alighting with her long legs on each side of the large, soft body, seizes it by the neck with her mandibles, and holds it fast. Now the caterpillar, stimulated doubtless by the painful, or at least unwelcome nip, struggles with redoubled energy; but it is beneath its oppressor, who, straddling over