mud is collected, almost the size of a pea. Taking the load in its teeth, the insect flies off, adds a layer to its building and soon returns to collect another pellet. The same work is pursued as long as the earth remains sufficiently wet, during the hottest hours of the day, for there is always some builder looking about for mortar. But the most frequented spot is in front of the great fountain in the village. Here there is a large trough where the people round about come to water their Mules. The constant trampling of the heavily-laden quadrupeds and the overflow of the water create a perpetual sheet of black mud which neither the heat of July nor the mighty blast of the mistral succeeds in drying. This bed of mire, so unpleasant for the passers-by, is beloved of the Pelopæi, who meet there from every part of the neighbourhood. You seldom pass before the noisome puddle without seeing some of them gathering their pellets amid the hoofs of the Mules slaking their thirst. The places exploited are enough in themselves to tell us that the mortar is collected ready-made, fit for immediate use without any further preparation than a vigorous kneading which gets rid of the lumps and makes the whole into a homogeneous mass. Other builders in clay, the Mason-bees, for instance, scrape up the dust on the highway and moisten it with saliva to convert it into a plastic material which will harden like stone by virtue of certain chemical properties of the salivary fluid. They set to work like the bricklayer, who mixes his mortar and his plaster by adding water in small quantities. The Pelopæus does not practise this art; the secret of chemical action is denied her; and the mud is employed just as it is picked up. To make sure of this, I stole a few pellets from the busy collectors and, on comparing them with other pellets gathered in the same place and rolled by my own fingers, found no difference between them in appearance or in properties. The result of this comparison is confirmed by an examination of the nest. The structures of the Chalicodomæ are solid masonry, capable of resisting without any protection the prolonged action of rain and snow; those of the Pelopæi are flimsy work, devoid of cohesion and absolutely unfitted to withstand the vicissitudes of the open air. A drop of water laid upon their surface softens the spot touched and reduces it to mud again, while a sprinkling equal to an average shower turns it into pap. They are nothing more than dried slime and become slime again as soon as they are wetted.