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Show 208 INSTINCT. (CHA.P. VII. of success in any family of bees. Of course the success of any species of bee n1ay be. dependent ?n t~e .nun1ber 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 circuinstance 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 com1nunity 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 humblebee, if a slight n1odification of her instinct led her to make her waxen cells near together, so as to intersect a little ; for a "~an in common even to two adjoining cells, would save some little wax. l-Ienee it would continually be more and more advantageous to our humble-bee, if she . were to make her cells Inore 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 Inake her cells closer together, and n1ore regular fn 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 n1ake a comb as perfect as that of the hive-bee. Beyond this stage of perfection in architecture, natural selection could not lead; for the co1nb of the hive-bee, as far as we can see, is absolutely perfect in economising wax. Thus, as I believe, the 1nost wonderful of all known instincts, that of the hive-bee, can be explained by natural selection having taken ad vantage 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 cou1.·se, no more knowing that they swept their spheres at one particular distance from eaeb other, than they know what CHA.l'. VII.] NEUTER INSECTS. 209 are the several angles of the hexagonal prisms and of th~ basal rhon1bic plates. The motive power of the process of natural selection having been econo1ny 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 eonomical 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 theory of natural seleetion,cases, in which we cannot see how an instinct could possibly have originated; cases, in which no intermediate gradations are known to exist; cases of instinct of apparently such trifling importance, that they could hardly have been acted on by natural selection; cases of instincts ahnost identically the same in animals so remote in the scale of nature, that we cannot account for their similarity by inheritance frmn a common parent, and must therefore believe that they have been acquired by independent acts 0f natural selection. I will not here enter on these several cases, but will confine myself to one special difficulty, which at first appeared to me insuperable, and actually fatal to n1y whole theory. I allude to the neuters or sterile females in insect com1nunities: for these neuters often differ widely in instinct and in structure from both the males and fertile fe1nales, and yet, from being sterile, they cannot propagate their kind. The subject well deserves to be discussed at great length, but I will here take only a single case, that of working or sterile ants. I-Iow the workers have been rendered sterile is a difficulty; but not much greater than that of any other striking ·modification of structure; for it can be shown that some inseuts and other articulate animals in a state of nature occasionally become sterile ; and if such insects had been social, and it had been profitable to the community, that a nu1nber should have been apnually born capable of work, but incapable of procreation, I can see no very great difficulty in this being effected by natural selection. But I must pass over this pre- |