In order to assure himself directly of the reality of his supposition, Réaumur tested the water which a fly, that he says "had got drunk on sugar," had brought back to the end of its trunk; he found this to be sugar and water. Also, having given a fly currant-jelly, he observed, after it had sufficiently gorged itself, several drops of red liquid in its trunk, and having tasted it, found it had the flavour which, from its appearance, he guessed it would have. The illustrious observer, who had already made all these discoveries on the formation and functions of the trunks of insects, often reflected on the fact that the liquors of which flies are most fond are enclosed under the skin of certain fruits, such as pears, plums, grapes, &c., or even under the skin of some animals of which they suck the blood. In order that the trunk of a fly may act under such circumstances, it is necessary for it to pierce and open the skin. If this is the case, flies ought to be possessed of a lancet. He looked a long time for this lancet, and at last found it. It is situated on the upper side of the part of the trunk which is terminated by the lips; it is placed in a fleshy groove, and is enclosed in a case. It has a very fine point, and is of light colour (Fig. 61). The point is situated in the opening which is to be seen between the lips of the trunk, at its anterior end, through which liquids may pass. That is the only opening of the lips; and the sucker which takes up the liquid is the same part which we just now called the case of the lancet. Réaumur is so interesting an author that it is difficult to cease quoting him; but we must continue our review of the principal kinds of Diptera. The genus _Musca_ (fly), in which Linnæus comprised the immense series of Diptera, with the exception of the _Tipulidæ_, the _Tabanidæ_, the _Asilidæ_, the _Bombylidæ_, and the _Empidæ_, is now reduced to the House Fly and a few resembling it. The habits of these troublesome companions are in conformity with the two great principles of animal life, that is, eating and propagating their species. Flies feed principally on fluids which exude from the bodies of animals; that is, sweat, saliva, and other secretions. They also seek vegetable juices; and they may be seen in our houses to feed eagerly on fruits and sweet substances. [Illustration: Fig. 61.--Lancet of the Meat Fly.] [Illustration: Fig. 62.--House Fly (_Musca domestica_).] The common flies deposit their eggs on vegetables, and particularly on fungi in a state of decomposition, on dung-heaps, cow dung, &c. They are essentially parasites, settling on both man and beast, to suck up the fluid substances which are diffused over the surface of their bodies. In our dwellings they eat anything that will serve to nourish them. Generation succeeds generation with the greatest rapidity.