PASSING to the insect world, we find the same principle carried out by the now familiar Mason-wasp (_Odynerus murarius_), some of whose nests are represented in the illustration. This insect makes a burrow, and at the bottom of it deposits an egg, together with a number of little caterpillars on which the grub, when hatched, will feed. The mother Wasp is not allowed to pursue this task without taking precautions against the admission of enemies to her burrow, especially the ichneumon-flies. As may be inferred from its popular name, the Sand-wasp always selects a sandy spot for its burrow, and generally chooses a piece of tolerably hard sandstone, which it is able to bite into little pellets, aided by a kind of liquid which it secretes. The following account of the manner in which the Mason-wasp forms and defends its home is taken from the invaluable “Insect Architecture,” by Rennie. The author begins by describing the form and depth of the burrow, and the soil in which it is made. He then proceeds to show the wonderful manner in which the mother Wasp purveys food for the use of her future young whom she will never see. Guided by instinct, she places in the burrow exactly the number of caterpillars which the young Mason-wasp will have to consume before it attains its perfect condition. It is believed that she partially paralyzes them with her sting before placing them in the burrow. At all events, when they are once packed away, they never move, so that the tiny Wasp grub can feed upon them quite at its leisure. Here is Rennie’s account of the Sand-wasp and her burrow-making:-- “When this wasp has detached a few grains of the moistened sand, it kneads them together into a pellet about the size of one of the seeds of a gooseberry. “With the first pellet which it detaches, it lays the foundation of a round tower, as an outwork, immediately over the mouth of its nest. Every pellet which it afterwards carries off from the interior is added to the wall of this outer round tower, which advances in height as the hole in the sand increases in depth. Every two or three minutes, however, during these operations, it takes a short excursion, for the purpose probably of replenishing its store of fluid wherewith to moisten the sand. Yet so little time is lost, that Réaumur has seen a mason-wasp dig in an hour a hole the length of its body, and at the same time build as much of its round tower. “For the greater part of its height this round tower is perpendicular, but towards the summit it bends into a curve, corresponding to the bend of the insect’s body, which, in all cases of insect architecture, is the model followed. The pellets which form the walls of the tower are not very nicely joined, and numerous vacuities are left between them, giving it the appearance of filigree-work.