the origin of species(物种起源)-第51章
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ork; by supposing masons first to pile up a broad ridge of cement; and then to begin cutting it away equally on both sides near the ground; till a smooth; very thin wall is left in the middle; the masons always piling up the cut…away cement; and adding fresh cement; on the summit of the ridge。 We shall thus have a thin wall steadily growing upward; but always crowned by a gigantic coping。 From all the cells; both those just commenced and those completed; being thus crowned by a strong coping of wax; the bees can cluster and crawl over the comb without injuring the delicate hexagonal walls; which are only about one four…hundredth of an inch in thickness; the plates of the pyramidal basis being about twice as thick。 By this singular manner of building; strength is continually given to the comb; with the utmost ultimate economy of wax。
It seems at first to add to the difficulty of understanding how the cells are made; that a multitude of bees all work together; one bee after working a short time at one cell going to another; so that; as Huber has stated; a score of individuals work even at the commencement of the first cell。 I was able practically to show this fact; by covering the edges of the hexagonal walls of a single cell; or the extreme margin of the circumferential rim of a growing comb; with an extremely thin layer of melted vermilion wax; and I invariably found that the colour was most delicately diffused by the bees as delicately as a painter could have done with his brush by atoms of the coloured wax having been taken from the spot on which it had been placed; and worked into the growing edges of the cells all round。 The work of construction seems to be a sort of balance struck between many bees; all instinctively standing at the same relative distance from each other; all trying to sweep equal spheres; and then building up; or leaving ungnawed; the planes of intersection between these spheres。 It was really curious to note in cases of difficulty; as when two pieces of comb met at an angle; how often the bees would entirely pull down and rebuild in different ways the same cell; sometimes recurring to a shape which they had at first rejected。
When bees have a place on which they can stand in their proper positions for working; for instance; on a slip of wood; placed directly under the middle of a comb growing downwards so that the comb has to be built over one face of the slip in this case the bees can lay the foundations of one wall of a new hexagon; in its strictly proper place; projecting beyond the other completed cells。 It suffices that the bees should be enabled to stand at their proper relative distances from each other and from the walls of the last completed cells; and then; by striking imaginary spheres; they can build up a wall intermediate between two adjoining spheres; but; as far as I have seen; they never gnaw away and finish off the angles of a cell till a large part both of that cell and of the adjoining cells has been built。 This capacity in bees of laying down under certain circumstances a rough wall in its proper place between two just…commenced cells; is important; as it bears on a fact; which seems at first quite subversive of the foregoing theory; namely; that the cells on the extreme margin of wasp…combs are sometimes strictly hexagonal; but I have not space here to enter on this subject。 Nor does there seem to me any great difficulty in a single insect (as in the case of a queen…wasp) making hexagonal cells; if she work alternately on the inside and outside of two or three cells commenced at the same time; always standing at the proper relative distance from the parts of the cells just begun; sweeping spheres or cylinders; and building up intermediate planes。 It is even conceivable that an insect might; by fixing on a point at which to commence a cell; and then moving outside; first to one point; and then to five other points; at the proper relative distances from the central point and from each other; strike the planes of intersection; and so make an isolated hexagon: but I am not aware that any such case has been observed; nor would any good be derived from a single hexagon being built; as in its construction more materials would be required than for a cylinder。
As natural selection acts only by the accumulation of slight modifications of structure or instinct; each profitable to the individual under its conditions of life; it may reasonably be asked; how a long and graduated succession of modified architectural instincts; all tending towards the present perfect plan of construction; could have profited the progenitors of the hive…bee? I think the answer is not difficult: it is known that bees are often hard pressed to get sufficient nectar; and I am informed by Mr。 Tegetmeier that it has been experimentally found that no less than from twelve to fifteen pounds of dry sugar are consumed by a hive of bees for the secretion of each pound of wax; so that a prodigious quantity of fluid nectar must be collected and consumed by the bees in a hive for the secretion of the wax necessary for the construction of their combs。 Moreover; many bees have to remain idle for many days during the process of secretion。 A large store of honey is indispensable to support a large stock of bees during the winter; and the security of the hive is known mainly to depend on a large number of bees being supported。 Hence the saving of wax by largely saving honey must be a most important element of success in any family of bees。 Of course the success of any species of bee may be dependent on the number of its parasites or other enemies; or on quite distinct causes; and so be altogether independent of the quantity of honey which the bees could collect。 But let us suppose that this latter circumstance determined; as it probably often does determine; the numbers of a humble…bee which could exist in a country; and let us further suppose that the community lived throughout the winter; and consequently required a store of honey: there can in this case be no doubt that it would be an advantage to our humble…bee; if a slight modification of her instinct led her to make her waxen cells near together; so as to intersect a little; for a wall in common even to two adjoining cells; would save some little wax。 Hence it would continually be more and more advantageous to our humble…bee; if she were to make her cells more and more regular; nearer together; and aggregated into a mass; like the cells of the Melipona; for in this case a large part of the bounding surface of each cell would serve to bound other cells; and much wax would be saved。 Again; from the same cause; it would be advantageous to the Melipona; if she were to make her cells closer together; and more regular in every way than at present; for then; as we have seen; the spherical surfaces would wholly disappear; and would all be replaced by plane surfaces; and the Melipona would make a comb as perfect as that of the hive…bee。 Beyond this stage of perfection in architecture; natural selection could not lead; for the comb of the hive…bee; as far as we can see; is absolutely perfect in economising wax。
Thus; as I believe; the most wonderful of all known instincts; that of the hive…bee; can be explained by natural selection having taken advantage of numerous; successive; slight modifications of simpler instincts; natural selection having by slow degrees; more and more perfectly; led the bees to sweep equal spheres at a given distance from each other in a double layer; and to build up and excavate the wax along the planes of intersection。 The bees; of course; no more knowing that they swept their spheres at one particular distance from each other; than they know what are the several angles of the hexagonal prisms and of the basal rhombic plates。 The motive power of the process of natural selection having been economy of wax; that individual swarm which wasted least honey in the secretion of wax; having succeeded best; and having transmitted by inheritance its newly acquired economical instinct to new swarms; which in their turn will have had the best chance of succeeding in the struggle for existence。
No doubt many instincts of very difficult explanation could be opposed to the