After choosing a boulder, she comes with a pellet of mortar in her mandibles, and arranges it in a ring on the surface of the pebble. The forefeet, and above all the mandibles, which are her most important tools, work the material, which is kept plastic by the gradually disgorged saliva. To consolidate the unbaked clay, angular pieces of gravel, as large as a small bean, are worked in singly on the outside of the still soft mass. This is the foundation of the edifice. Other layers are added until the cell has the required height of three or four centimetres. The masonry is formed by stones laid on one another and cemented with lime, and can stand comparison with our own. True, to economise labour and mortar, the bee uses coarse materials,—large bits of gravel, which in her case answer to hewn blocks. They are chosen singly—very hard ones, almost always with angles which, fitted together, give mutual support, and add solidity to the whole. Layers of mortar, sparingly used, hold them together. The outside of the cell thus assumes the look of a piece of rustic architecture, in which stones project with their natural inequalities; but over the inside, which requires a smoother surface in order not to wound the tender skin of the larva, is spread a wash of pure mortar—artlessly, however, as if by broad sweeps of a trowel; and when it has eaten up its honey paste, the grub takes care to make a cocoon and hang the rude wall of its abode with silk. The Anthophora and Halictus, whose larvæ spin no cocoon, varnish the inside of their earthen cells delicately, giving them the polish of worked ivory.