But, so far, the design is still only in its crude, initial stage. The upright comb, consisting of a double pile of round cells, back to back, with one flat base between, although a great advance on the single sheet of horizontal cells, is yet mechanically and economically deficient. The round cells leave useless interstices, which take much wax in the filling; while the flat bottoms do not coincide with the form of the larvæ, and thus still more space is wasted. Clearly, improvement can only come by altering the shape of the cell; and now the bee seems to have asked herself-and triumphantly answered—an extremely complex question. She knew how much internal cell-space each larva required for growth. The problem, therefore, was this: of what shape, nearly approaching the cylindrical, ought such a cell to be made, which would ensure the right dimensions, but which would occupy the least possible room, have the greatest possible strength, consume the least possible material in its manufacture, and possess the property that a number of similar cells could be built up in a double vertical plane, leaving no interstices either between the cells or between the planes? There is only one solution to this problem; and the honey-bee found it—who shall say how many ages ago?—in the hexagon cell, with its base composed of three rhombs. The whole astounding ingenuity of the thing can only be realised when a piece of nearly perfect, new-made, virgin-comb has been closely examined. It will be at once seen that the hexagon cells combine together over the surface of the comb in absolute geometrical union, and that the six-sided form is round enough for all practical purposes. Looking into the cells on one side of the comb, it will be noted that their bases take the form of depressed pyramids, each made up of three diamond-shaped planes. [Picture: Honey-comb, transmitted light, showing arrangement of cells on both sides]