Her division is made by a dab of clay placed at right angles to the axis of the cylinder, at a distance from the bottom determined by the ordinary length of a cell. This wad is not a complete round; it is more crescent-shaped, leaving a circular space between it and one side of the tube. Fresh layers are swiftly added to the dab of clay; and soon the tube is divided by a partition which has a circular opening at the side of it, a sort of dog-hole through which the Osmia will proceed to knead the Bee-bread. When the victualling is finished and the egg laid upon the heap, the hole is closed and the filled-up partition becomes the bottom of the next cell. Then the same method is repeated, that is to say, in front of the just completed ceiling a second partition is built, again with a side-passage, which is stouter, owing to its distance from the centre, and better able to withstand the numerous comings and goings of the housewife than a central orifice, deprived of the direct support of the wall, could hope to be. When this partition is ready, the provisioning of the second cell is effected; and so on until the wide cylinder is completely stocked.
The building of this preliminary party-wall, with a narrow, round dog-hole, for a chamber to which the victuals will not be brought until later is not restricted to the Three-horned Osmia; it is also frequently found in the case of the Horned Osmia and of Latreille's Osmia. Nothing could be prettier than the work of the last-named, who goes to the plants for her material and fashions a delicate sheet in which she cuts a graceful arch. The Chinaman partitions his house with paper screens; Latreille's Osmia divides hers with disks of thin green cardboard perforated with a serving-hatch which remains until the room is completely furnished. When we have no glass houses at our disposal, we can see these little architectural refinements in the reeds of the hurdles, if we open them at the right season.
By splitting the bramble-stumps in the course of July, we perceive also that the Three-pronged Osmia, notwithstanding her narrow gallery, follows the same practice as Latreille's Osmia, with a difference. She does not build a party-wall, which the diameter of the cylinder would not permit; she confines herself to putting up a frail circular pad of green putty, as though to limit, before any attempt at harvesting, the space to be occupied by the Bee-bread, whose depth could not be calculated afterwards if the insect did not first mark out its confines. Can there really be an act of measuring? That would be superlatively clever. Let us consult the Three-horned Osmia in her glass tubes.
The Osmia is working at her big partition, with her body outside the cell which she is preparing. From time to time, with a pellet of mortar in her mandibles, she goes in and touches the previous ceiling with her forehead, while the tip of her abdomen quivers and feels the pad in course of construction. One might well say that she is using the length of her body as a measure, in order to fix the next ceiling at the proper distance. Then she resumes her work. Perhaps the measure was not correctly taken; perhaps her memory, a few seconds old, has already become muddled. The Bee once more ceases laying her plaster and again goes and touches the front wall with her forehead and the back wall with the tip of her abdomen. Looking at that body trembling with eagerness, extended to its full length to touch the two ends of the room, how can we fail to grasp the architect's grave problem? The Osmia is measuring; and her measure is her body. Has she quite done, this time? Oh dear no! Ten times, twenty times, at every moment, for the least particle of mortar which she lays, she repeats her mensuration, never being quite certain that her trowel is going just where it should.
Meanwhile, amid these frequent interruptions, the work progresses and the partition gains in width. The worker is bent into a hook, with her mandibles on the inner surface of the wall and the tip of her abdomen on the outer surface. The soft masonry stands between the two points of purchase. The insect thus forms a sort of rolling-press, in which the mud wall is flattened and shaped. The mandibles tap and furnish mortar; the end of the abdomen also pats and gives brisk trowel-touches. This anal extremity is a builder's tool; I see it facing the mandibles on the other side of the partition, kneading and smoothing it all over, flattening the little lump of clay. It is a singular implement, which I should never have expected to see used for this purpose. It takes an insect to conceive such an original idea, to do mason's work with its behind! During this curious performance, the only function of the legs is to keep the worker steady by spreading out and clinging to the walls of the tunnel.
The partition with the hole in it is finished. Let us go back to the measuring of which the Osmia was so lavish. What a magnificent argument in favour of the reasoning-power of animals! To find geometry, the surveyor's art, in an Osmia's tiny brain! An insect that begins by taking the measurements of the room to be constructed, just as any master-builder might do! Why, it's splendid, it's enough to cover with confusion those horrible sceptics who persist in refusing to admit the animal's 'continuous little flashes of atoms of reason!'
O common-sense, veil your face! It is with this gibberish about continuous flashes of atoms of reason that men pretend to build up science to-day! Very well, my masters; the magnificent argument with which I am supplying you lacks but one little detail, the merest trifle: truth! Not that I have not seen and plainly seen all that I am relating; but measuring has nothing to do with the case. And I can prove it by facts.
If, in order to see the Osmia's nest as a whole, we split a reed lengthwise, taking care not to disturb its contents; or, better still, if we select for examination the string of cells built in a glass tube, we are forthwith struck by one detail, namely, the uneven distances between the partitions, which are placed almost at right angles to the axis of the cylinder. It is these distances which fix the size of the chambers, which, with a similar base, have different heights and consequently unequal holding-capacities. The bottom partitions, the oldest, are farther apart; those of the front part, near the orifice, are closer together. Moreover, the provisions are plentiful in the loftier cells, whereas they are niggardly and reduced to one-half or even one-third in the cells of lesser height.
Here are a few examples of these inequalities. A glass tube with a diameter of 12 millimetres (.468 inch.—Translator's Note.), inside measurement, contains ten cells. The five lower ones, beginning with the bottom-most, have as the respective distances between their partitions, in millimetres:
11, 12, 16, 13, 11. (.429,.468,.624,.507,.429 inch.—Translator's Note.)