Evidently, this is a case of mutual accommodation in the political economy of the ants and aphides: a free interchange of services between the ant as consumer and the aphis as producer. Why the aphides should have acquired the curious necessity for getting rid of this sweet, sticky, and nutritious secretion nobody knows with certainty; but it is at least quite clear that the liquid is a considerable nuisance to them in their very sedentary and monotonous existence--a waste product of which they are anxious to disembarrass themselves as easily as possible--and that while they themselves stand to the ants in the relation of purveyors of food supply, the ants in return stand to them in the relation of scavengers, or contractors for the removal of useless accumulations. Everybody knows the aphides well by sight, in one of their forms at least, the familiar rose aphis; but probably few people ever look at them closely and critically enough to observe how very beautiful and wonderful is the organisation of their tiny limbs in all its exquisite detail. If you pick off one good-sized wingless insect, however, from a blighted rose-leaf, and put him on a glass slide under a low power of the microscope, you will most likely be quite surprised to find what a lovely little creature it is that you have been poisoning wholesale all your life long with diluted tobacco-juice. His body is so transparent that you can see through it by transmitted light: a dainty glass globe, you would say, of emerald green, set upon six tapering, jointed, hairy legs, and provided in front with two large black eyes of many facets, and a pair of long and very flexible antennae, easily moved in any direction, but usually bent backward when the creature is at rest so as to reach nearly to his tail as he stands at ease upon his native rose-leaf. There are, however, two other features about him which specially attract attention, as being very characteristic of the aphides and their allies among all other insects. In the first place, his mouth is provided with a very long snout or proboscis, classically described as a rostrum, with which he pierces the outer skin of the rose-shoot where he lives, and sucks up incessantly its sweet juices. This organ is common to the aphis with all the other bugs and plant-lice. In the second place, he has half-way down his back (or a little more) a pair of very peculiar hollow organs, the honey tubes, from which exudes that singular secretion, the honey-dew. These tubes are not found in quite all species of aphides, but they are very common among the class, and they form by far the most conspicuous and interesting organs in all those aphides which do possess them.