If one of these tracheæ be removed and placed under the microscope, it will be seen to be constructed in a manner exactly similar to that which has been described. Within the membrane which forms the tube proper there is a very fine, but very strong thread, which is coiled exactly like the wire spring. It is not attached to the membrane, and so strong is it that, although it is all but invisible to the naked eye, it can be drawn out as shown in the left-hand figure of the illustration. If laid on a piece of glass, it immediately tries to recoil itself, and for some little time will twist and curl about as if it were alive. [Illustration: TRACHEA OF DRAGON-FLY LARVA.] [Illustration: TUBE OF HOOKAH.] * * * * * ON the above illustration are two similar examples of the spiral thread with a flexible tube. The right-hand figure represents one of the many forms of the water-pipe, whether known as Hookah, Narghile, or Hubble-bubble. In the simpler forms of this pipe, such as the latter, the inhaling-tube is quite straight, and the bowl is held in the hands of the smoker. In the more refined pipe, however, the tube is very long, flexible, and made elastic by an inner spiral wire. Perhaps the reader may remember that the larva of the Dragon-fly is a most remarkable creature in consequence of its methods of propulsion and respiration. The water is taken into the interior of the body through a peculiarly formed aperture, and then ejected with such violence as to drive the body forward on the same principle as that which causes a rocket to ascend. The figure on the left hand of the illustration is a representation of the abdomen of this larva rather magnified, and opened so as to show the interior. On either side run the two principal breathing-tubes, through the delicate membranes of which the spiral thread can plainly be seen. These tubes are connected with a smaller set, and they with a still smaller, so that at last they are of such tenuity that they can scarcely be distinguished without the use of a glass. But, however small they may be, they are always fitted with the spiral thread. * * * * * WE now come to the cases where the membrane is supported by a series of rings, and not by a single spiral wire. In the right-hand division of the illustration are two specimens of objects which shall be nameless, but which were drawn per special favour at a milliner’s shop. Although the day has now happily gone by when the larger object was in general wear, and seemed to be irrepressively increasing in dimensions, certain modifications of it, under various names, have made their appearance in almost every book of fashions and every large milliner’s shop. Here we have the external membrane made of linen, calico, merino, or similar material, distended by a number of elastic rings set at tolerably even distances from each other.