Automatically perhaps—that is to say, between the lines—we may gather Mr. Buckton’s opinion of the automatic theory. There are some theories which seem held, like dykes or barriers, to prevent the sea from getting in. One doesn’t want the sea to get in, because it would swamp such a lot of things, which, although quite artificial, one is not prepared to part with, but one doesn’t believe in the barrier except for that particular purpose to which it is applied. The automatic theory in regard to animals is a case in point. Scientific men make use of it in order to keep out another, which they don’t want to have to admit, though they do, as a fact, believe in it. This, again, one can read between the lines whenever they give any account of their observations on this or that animal, whether it be dog or elephant, ants or something much lower down in the scale—rotifers, for instance, or amœba in the ocean of a watch-glass. One sees what they really mean very well then, though they may not themselves be aware of it, but they are never in the least _convincing_ when they air their automatic theory. Aphides, as may have been gathered incidentally, feed wholly upon the juices or sap of plants. Active _ab ovo_ (which means from the egg), “their occupation,” says Mr. Buckton, “is to grow as fast as possible,” and with a view to this end the rostrum or beak, with its enclosed sucking or pumping apparatus, is fully developed from the very commencement, “often, indeed, to such an abnormal extent that it forms an awkward appendage, trailing behind the body whilst walking.”[43] The insect does not, however, walk much, but, settling itself down on the twig or stem where, perhaps, it first saw the light, pierces the bark with the instrument thus provided for it, and commences to suck up the sap into its mouth. This is not a process which can be indulged in with impunity to the plant, especially since Aphides reside in great societies upon the same one, and turn their attention to every part of it, not even excepting the roots. Troops of small Aphides, in fact, have sometimes been found in the pips of large codling apples. In consequence of this excessive drain upon their fluids, which is as though our own blood were to be sucked, plants thus invaded by Aphides become greatly weakened, and their young shoots and leaves have a distorted appearance in consequence. Others, either through this cause alone, or in consequence of some poison or acid injected by the Aphis, have gall-like excresences produced upon them. These have a hollow interior, into which the Aphides penetrate, and there take up their residence. Such swellings thus become their houses, and therefore, since it is a great advantage to the Aphides to be sheltered in this way, it is possible that some special instinct through the exercise of which the tree is thus affected, may have been implanted in them by the action of natural selection.