The bottoms and sides of the cells are made of wax as thin as a sheet of writing-paper; but as walls of this thinness at the entrances would break down under the weight of the constantly passing insects, the margin at the opening of each cell is made four or five times thicker than the walls. Then, as the cells are lengthened, this thickness is reduced, always remaining the same, however, at the actual margins. Dr. Barclay also discovered that, though the tenuity of the divisions is so great, each, in point of fact, consists of two distinct layers agglutinated together. This gives, again, an increase of strength, as any practical builder would know who, in his "bressummers," adopts the same method of attaining lightness and power of sustaining great weights. [Illustration: Fig. 17.--Diagram Showing Slope of Cells.] The actual size of the cells in a hive varies considerably, as we might expect. Without regarding those for queen-progeny, we should anticipate that those in which young drones are to be developed would be considerably larger than those prepared for workers. This is, indeed, the case. But as an abrupt change from the one kind to the other would be impossible without waste, the bees prudently graduate the difference by interposing a suitable series of intermediate sizes, whose bottoms, of course, have to depart from the normal conditions, and sometimes consist of two rhomboids and two hexagons, varying in size and form, and corresponding with four, instead of three, opposite cells. In these, stores are often found, instead of brood. If eggs are laid in them, they are generally those which will develop into males, and the space for development being smaller than usual, the drones occupying such cells are not so large as the average size. As a rule, the hexagonal ends of twenty-seven worker cells, or nineteen drone cells, occupy a surface of one square inch. All the cells lie not quite horizontally, but sloping slightly downwards from the mouth towards the bases. This arrangement is designed to prevent the honey from easily flowing out. As the cells are filled with the liquid, the lower edge of each is first raised, and, in due time, the whole of the once open end is sealed over with a coating of wax mixed with a little propolis. This covering not only keeps the contents from running out, but prevents fermentation or candying, from contact with the air. Each comb consists of a double layer of cells, back to back, and forming a sort of flat cake. At first this is lenticular in shape, the middle part being advanced rather more rapidly than the ends.