CHAPTER VI.
SPIRAL AND RINGED TISSUES.—VARIOUS SPRINGS IN NATURE AND ART
Spiral Tissues, and their Structure and Uses.—The movable Gas-lamp.—Elastic Tubes.—Breathing-tubes of Insects, and their Spiral Wire.—Ringed Tissues and their varied Structure.—Ringed Tissues applied to modern Dress.—Chinese and Japanese Lanterns.—Proboscis of the House-fly.—Trachea of various Animals.—Mutual Tendency of Rings and Spirals towards each other.—Fibres of the Yew-tree.—Diving and Divers.—Principle of the Diving-bell.—How it is supplied with Air.—Structure of the Air-tubes.—Nests of the Water-spider.—Diving by means of Tubes.—Larva of the Drone-fly, and its Mode of breathing.—How to examine them.—Leaping Springs.—The Skip-jack in Nature and Art.—Skip-jack or Click Beetles.—The Spring-tail, Grasshopper, Kangaroo, Gerboa, and other Jumping Creatures.
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.
Diving and Divers
It has already been mentioned that the flexible tubes used by modern divers are constructed on the model of several structures belonging to the animal and vegetable kingdoms.
We will now see how they are utilised.
In the earlier stages of the diver’s art the Diving-bell afforded the only means of gaining access to the bed of the sea, even in comparatively shallow waters. The mode in which this result was obtained was simple enough, and though it carried with it the germs of still greater improvements, was but limited and uncertain in its action.
The reader is probably aware that if a vessel be filled with air, no liquid can obtain admittance until a corresponding amount of air be set free. Suppose, for example, that an empty tumbler be inserted over a basin of very clean water, and pressed downwards, it will be found that scarcely any water will enter it, the air having taken up all the available space, and only allowing as much space as may be accounted for by its faculty of compression.
It is evident, therefore, that if an enlarged tumbler could be lowered to the bed of the sea, a man might be enclosed within it, and for a time be able to support life by means of the air contained within the “bell,” as this enlarged tumbler was popularly called.
It is equally evident that within a short time the air within the bell must be exhausted, and that, unless a fresh supply could be introduced, the diver within the bell would be as effectively drowned as if there were no bell at all.
The accompanying illustration is a kind of chart, so to speak, of the mode in which air was formerly supplied to the bell.
On the right hand is seen a section of the Diving-bell itself, together with the seat on which the divers can rest. There is also an escape-valve at the top of the bell, by which the vitiated air can pass away; but, as it is not essential to the subject in hand, and is rather complicated in structure, it has been omitted.
Immediately on the left of the bell is a cask, to which several heavy weights are attached. This cask contained compressed air, and, after it was lowered by the side of the bell, the end of the flexible tube was taken into the bell, the tap turned, and the compressed air rushed into the bell, taking the place of that which had been exhausted by respiration, and was allowed to pass through the escape-valve. I may mention that the divers unexpectedly discovered that, when they were breathing compressed air, they could dispense with respiration for a wonderfully long time, the amount of oxygen taken in at a single breath being enough to renovate the blood more than could be done by several ordinary inspirations.
On the left hand of the illustration is seen a sketch of the nest of the now familiar Water-spider (Argyronetra aquatica), taken from some specimens in my possession.
The Water-spider is really a remarkable being. Itself a denizen of air, breathing our earthly atmosphere just as we do, and as capable of being drowned as ourselves, it nevertheless passes nearly the whole of its existence under water, and in that strange locality lays its eggs and rears its young. How this wonderful feat is performed we shall now see.
When the female Water-spider wishes to deposit her eggs, she looks out for a suitable locality, and, being a good diver, tests the various aquatic herbage until she has found a favourable spot, and then sets to work on her remarkable nest, which I believe is quite original in zoology.
After stretching a few stout threads by way of a scaffolding, she attaches to the plant a small silken cell, shaped very much like an acorn, but not so large. Ascending to the surface of the water, she contrives to clasp a bubble of air between her last pair of legs, and, laden with this airy treasure, dives below.
As soon as she has reached the entrance to the cell, which is always below, she loosens her hold of the air-bubble. It at once rises into the cell, and expels a proportionate amount of water. Not many of these journeys are required before the nest is filled with air, and then the diminutive architect spends the greater part of its time in holding on to the mouth of the little diving-bell, and supporting life by means of the air within it.
This nest, as the reader will see, is an exact representation of the various diving schemes in which air-bells are the chief portions of the machinery, although the air is conducted into them after a different fashion.
We now come to another mode of diving, in which the bell is practically superseded by the flexible tube, which allows to the diver far more range than can be obtained by the bell. In this case the diver wears a peculiar dress, the chief part of which is a helmet so constructed that air can be introduced to it from above the surface of the water, and, after respiration, can escape by means of a valve.
Air is pumped into the tube by assistants above water, and, as the tube is long and elastic, the diver can move about with considerable freedom. As is the case with the diving-bell, the diver’s tube is strengthened by an internal spiral wire, so that it is always open, however it may be bent or twisted.
The right-hand figure of the illustration represents the diver examining part of a sunken vessel. The tube through which he breathes is seen passing to the surface of the water, and so is the line by which he gives his signals to his comrades above. In his hand he holds a lamp which can burn for a limited time, being connected by a smaller but similarly constructed tube to a vessel of compressed air.
On the left hand of the same illustration are shown the curious Rat-tail Maggots, as they are popularly called. They are the larvæ of the common Drone-fly (Eristalis tenax), which is so common towards the end of summer, and looks so curiously like a bee.
These creatures pass their larval life buried in the mud and below the surface of the water, and yet are obliged to breathe atmospheric air. This they do by means of the long appendages which have gained for them the name of Rat-tails. These “tails” are very elastic, and are capable of elongation and contraction to a wonderful extent.
When the creature is undisturbed, it lies buried in the mud with its head downwards, and its tail extended so that it reaches the surface of the water. Within this tail are two air-tubes, which are connected with the principal tracheæ, which have already been mentioned. They are wonderfully elastic, and, when the tail is extended to its utmost limit, are nearly straight. When, however, the tail is contracted, the tubes become self-coiled by their own elasticity, and shrink into the base of the tail.
As the tail is very transparent, it is easy to see how these movements are conducted. The larvæ, which may be found in almost any stagnant water, should be placed in a tall and narrow glass. Some mud should be placed at the bottom of the glass, which should then be filled with water to the depth of three inches or so.
When the mud has quite subsided, and the water become clear, the long slender tails of the larvæ will be seen so elongated that their tips reach just above the surface of the water. A magnifying-glass will easily show the two tubes within the tail.
Let the glass be but slightly tapped, and all the tail is withdrawn in a moment, so as to be out of reach of external danger. The magnifying-glass will then show the two tubes lying contracted in the base of the tail, and taking astonishingly little space, considering the amount of elongation which they can sustain. And, on examining the various bends and curves of the tubes, the value and power of the spiral spring will at once be seen. True, they are very small, but in Nature all things go by comparison, and our whole earth itself is as a grain of sand upon the seashore among the grandeurs of the visible universe.
The Leaping Spring
The last of the springs which can be mentioned in this work are those which are used for leaping purposes.
The figure on the right hand represents the common Spring-jack or Skip-jack with which children are always so much amused. It consists of a flattened piece of wood called the “tongue,” which is inserted into a twisted string, so that it forms a tolerably powerful spring. When twisted round, and then suddenly released, it strikes against the ground with such force that the whole machine is thrown into the air.
Sometimes the Skip-jack is made of a fowl’s merrythought, as shown in the illustration; sometimes of the breast-bone of a goose; and sometimes of a piece of wood cut into the semblance of a frog, and painted. In all cases, however, the machinery is practically the same. I may mention en passant that these frog Skip-jacks are most acceptable presents to savage chiefs in many parts of the world, and that the most powerful and venerable warriors are as delighted with these toys as any European child of six years old.
Now we will turn to Nature, and see what she has in the way of Skip-jacks.
All entomologists will at once have before their minds the vast groups of Skip-jack Beetles, technically termed Elateridæ, and also known as Click-beetles, from the sharp clicking sound which they produce when in the execution of their curious gymnastics. To this group belong the fire-flies of warm countries, and it may be mentioned that the larvæ of some of our species are too familiar to the agriculturist under the name “wireworm.”
All these beetles have very short legs and very long bodies, so that if they should fall on their backs on a smooth surface, they could not recover themselves. Now, as they, when discovered, instinctively try to save themselves by falling to the ground, it is evident that some means must be used to enable them to regain their position. This is found in a most curious apparatus.
Attached to the “prothorax” is a rather long, pointed, and very elastic projection exactly corresponding with the tongue of the Skip-jack. The end of this tongue fits into a groove in the “sternum.”
When the beetle falls on its back, it curves its body as shown in the illustration, the tongue thus being freed from its groove. It then smartly springs the tongue back into its place with the sharp clicking sound already referred to, and does so with such force that it leaps into the air to some height.
Generally it falls on its feet, but if it should fail, it repeats the process. If one of these beetles be laid on a plate or similar smooth surface, it will skip ten or twelve times without stopping, and after a short rest will begin again.
There are some curious little beings, popularly called Spring-tails, which afford excellent examples of the Leaping Spring. Their exact place in the system of Nature is rather uncertain, some zoologists considering them as insects, while strict entomologists reject them. They are very small, and mostly of a darkish brown colour.
Plenty of them may be found under stones in damp spots, under bark, and in similar localities, though they are often found in houses, and have frequently traversed the paper on which I have been writing this book. Cellars are favourite localities of theirs, and a little flour sprinkled on a plate or piece of paper in a cellar is tolerably sure to attract them. Although they are certainly not more than the fifteenth of an inch in length, they may be at once recognised by their peculiar attitude, which very much resembles that of a dog or cat in its usual sitting posture.
As long as they are not disturbed they crawl about in a quiet manner, but if touched, or even alarmed, they suddenly make a tremendous leap, propelling themselves by means of a forked and elastic tail, doubled under their bodies, and acting just like the tongue of a Skip-jack.
Below the Skip-jack Beetle is shown the common Grasshopper, as an example of muscular leaping springs.
We all know what wonderful leaps the Grasshopper, Cricket, and all their kin can make, the leaping movement being evidently intended more as a means of defence than as an ordinary mode of locomotion. The same may be observed in the Kangaroos and Gerboas, which are content to use an ordinary walking pace when undisturbed, but when alarmed can make tremendous leaps, and outstrip almost any pursuer.
Even in Man, the Horse, the Dog, &c., which are most essentially leaping animals, the same principle is employed, the legs being used as muscular springs acted upon by the will of the owner.