Spiral and Ringed Tissues.
WE have now to consider the Spiral Tissue under another aspect, i.e. that of acting as the internal support of an exterior membrane. Ringed tissues are necessarily conjoined with the Spiral, as they both discharge the same office, and in some cases merge almost imperceptibly into each other in the same specimens. This is most beautifully shown in the proboscis of the common House-fly, to which reference will presently be made.
The subject is so large that only a comparatively small selection of examples can be made, the greater number belonging to Nature, and not to Art.
We will first take the common movable Gas-lamp, with its accompanying tube. It is at present the tube of which we have to treat, the gas itself being reserved for a future page.
It is necessary that, in order to enable the lamp to be moved from one spot to another, the tube through which the gas passes must be so constructed that if it be bent, or even coiled, it retains its form, and does not become flattened. In order to obtain this object, a very long thin wire is coiled spirally to a suitable length. Over this wire is sewn the casing of the tube, which is afterwards made waterproof with elastic varnish. A still simpler mode is by enclosing a spiral wire within a tube of vulcanised india-rubber. It will be seen, then, that by the elasticity of the spiral wire the tube must always retain its shape, no matter how much it may be bent.
On the right hand of the illustration are shown the movable Gas-lamp and tube, and a portion of the latter is given with its spiral wire partially unwound, in order to show its structure.
The large tubes which convey air to divers are made in the same manner, as they would not only succumb to the pressure of the water without the wire, but could not be dragged over obstacles or round corners without collapsing. It often happens that a diver is obliged, when surveying a sunken ship, to traverse the whole of her interior, descending ladder after ladder, and entering every cabin in the ship. This could not be done but for the internal coil of wire within the tube. Reference will presently be made to the subject of diving.
On the left hand is seen an object that looks something like a branch hollowed very thin. It is a magnified view of part of the Trachea or breathing-tube through which air is conveyed into the system of an insect. These breathing-tubes ramify to every portion of the body of an insect, even penetrating to the extremities of the antennæ, the wings, and the legs. It is obvious that as these organs are in tolerably constant movement, and the legs are much bent at every joint by the action of walking, the air-tubes which run through them must possess the same qualities as those of the gas-lamp and diver.
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.
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.
The two small objects represent the handy little paper lanterns so common in China and Japan. They are composed of an external coat of tough tissue paper, so thin that it allows the light to pass through it with tolerable freedom, and of an internal series of elastic rings, which not only support it and preserve its cylindrical shape, but allow it to be folded up flat when not wanted.
I possess a singularly ingenious lantern of this kind, made in Japan, and displaying the thoroughness of work which characterizes that nation. It is five inches in diameter, and the lantern itself is affixed at either end to a circular wooden cap the upper fitting over the lower. Consequently, when the lantern is shut, it is entirely enclosed between these two caps, which effectually preserve it from harm. It is delicately finished, and has no less than thirty rings, made of very narrow strips of bamboo. The upper cap has a little trap-door through which the candle can be admitted and trimmed, and in its centre is a small round hole for the passage of air.
In the left-hand division of the illustration are shown several examples of ringed and spiral tissues belonging to the vegetable world, in which the principle is exactly the same as that of the Chinese lantern, &c. That on the right hand is an example of simple rings within a membrane. The central figure shows a double spiral, which produces very much the appearance of a series of rings; and on the extreme left is an interesting example which shows the transition in the internal supports from spirals to rings.
I have already mentioned that the proboscis of the House-fly exhibits this modification. If one of these objects be placed under a moderate power microscope—the half-inch is quite enough—and examined, it will be seen that there are some large tracheæ, just like those of the Dragon-fly larva, on each side of the proboscis, and that, where the end is widened and flattened into a sort of disc, their place is taken by a set of very much smaller tracheæ, coming nearly to a point, and each being supported internally by a series of incomplete rings, shaped very much like the letter C. A slide containing this object well mounted can be purchased at any optician’s for a shilling.
The trachea, or windpipe, as we call it, of all vertebrate animals, man included, is formed on exactly the same principle, as any one may see by going to a butcher’s shop, and looking at the trachea, or windpipe, by which the lungs, or “lights,” as they are called, are suspended. Were it not for this structure, we should not be able to bend our necks or turn our heads.
The accompanying illustration shows the tracheæ of three well-known creatures. The left-hand figure is the trachea of an Ox, the central figure that of a Pig, and the right-hand figure that of a Goose. Mr. Tuffen West, who made the drawings, sent with them the following remarks:—
“The tracheæ of animals furnish some very interesting examples of variation in the form and arrangement of the rings. Their purpose, perhaps, one can but guess at in some cases; but doubtless, as being works of the Master Builder, careful study would be repaid.
“In the Ox the rings are very strong and close, and in form like a horse-shoe with the ends approximated.
“In the Pig the incomplete rings are broad at one part, and narrow on the opposite side, with a tendency to spiral arrangement. I imagine that this would make a very rigid tube, and, indeed, it feels so in the hand.
“Then, in the Goose, the narrowed lower part is that which is figured just before the trachea reaches the sternum. The (complete) rings are twice as broad in one half as in the other, and by the alternate disposition of these differing widths, a tube is formed of great flexibility fore and aft, but almost absolutely rigid in the lateral direction. This seems to be so marked an evidence of design as to be calculated to greatly raise our admiration.”
We have seen several examples of ringed tissues tending to the spiral form, and it is but natural that we should expect to find spiral tissues tending to the ring.
In the accompanying illustration the two left-hand figures represent the curiously modified ringed tissue which is to be found in the sugar-cane, the left-hand figure being much more magnified than the other.
The other figures represent four examples of vegetable spiral tissues, in which it will be seen that there is a tendency to form rings, and that if a number of rings were substituted for the spiral, and the object viewed in a slanting direction, it would be almost impossible to distinguish between the ring and the spiral.
Among the most remarkable of these examples are the two right-hand figures. That on the extreme right represents a spiral vessel taken from the so-called root, or “rhizome,” of the Water-lily, and the other is a similar vessel taken from a branch of the Yew-tree. It has been suggested that to this spiral structure is due the proverbial elasticity of the yew-tree, which has from time immemorial rendered it the best wood for the manufacture of bows.