Perhaps some of my readers may be acquainted with a saw which has of late years come into extensive use—namely, the Ribbon Saw, Cordon Saw, or Band Saw. This is an endless steel band toothed on one edge, and passing over two wheels. It has the advantage of being of almost any breadth, some being several inches wide, while others are mere narrow ribbons, barely the sixth of an inch wide. The fretwork of pianos and other articles of furniture is cut almost exclusively by the Cordon Saw. A thick piece of wood is cut of the requisite shape, and the upper and under surfaces planed quite true to each other. The pattern is traced on the upper surface, and a very narrow Cordon Saw is then applied to it, cutting completely through the thick block, and adapting itself to all the intricacies of the pattern. The block is then cut into thin slices, so that a number of pieces of fretwork can be made with comparative ease. To those who have been accustomed to cutting fretwork with the slow hand-saw, the Cordon Saw is simply fascinating, the slender steel ribbon cutting through the wood with wonderful rapidity and very little sound.
Beautiful as this invention is, it was long ago anticipated in Nature; and the Cordon Saws, which we shall now see, are armed with teeth many more in number, and far more complicated in detail, than those of any saw made by the hand of man. I allude to the Tooth-ribbon possessed by many of our common molluscs, such as the Limpet, the Whelk, the Periwinkle, the Slug, &c. The last mentioned of these creatures possesses a natural Cordon Saw with nearly twenty-seven thousand teeth, and scarcely a tooth that is not elaborately cut into secondary teeth.
As all these creatures have their teeth differently formed and set, according to the species, it will be impossible to describe them separately. I will therefore restrict myself to the Tooth-ribbon of the common Whelk, a specimen of which is now before me. When viewed through the microscope, it is found to consist of a flat membranous ribbon, on which are set three rows of teeth, those of the outer row being hooked, and those of the inner one plain.
The outer teeth are formed somewhat like the Hebrew letter כ, both of the points being very sharp, and the central part being furnished with two secondary teeth. All these teeth overlap each other, so that some care in manipulation is required before their form can be made out.
Along the centre of the tooth-ribbon run successive rows of small, lancet-shaped teeth, six in a row, so that altogether there are eight teeth in each row.
The power of this weapon is astonishing. Some of my readers may be aware that Whelks are carnivorous beings, and that they swarm upon any dead animal which may be found in the sea. Indeed, when we hear of the mutilations which take place on dead corpses after a shipwreck, and which are generally attributed to fishes, we may make up our minds that the real delinquents are the Whelks, together with various crustacea, and that the principal instrument in effecting such mutilation is the tooth-ribbon which has just been described.
The Whelks feed largely upon other molluscs, in spite of their shells. A periwinkle has a peculiarly hard shell, and yet Mr. Rymer Jones saw a Dog-whelk (Purpura lapillus) eat a periwinkle in a single afternoon, first boring a hole through its shell with the tooth-ribbon, and then, by means of the same weapon, licking it, so to speak, out of its shell.
The Periwinkle itself has a similar tooth-ribbon, and so have the Limpet and the pretty Top-shell. These creatures are vegetarians, but they are furnished with similarly armed tongues, and use them in the same way. Nothing is easier than to see these tooth-ribbons in use. When sea-water is kept in glass vessels, a green flocculence is sure to collect upon the glass and to render it opaque.
If, however, a few Periwinkles and Top-shells are placed in the tank, they immediately set to work at this confervoid growth, and by means of the tooth-ribbon sweep off the green substance, leaving the glass nearly clean. This movement can be seen with the naked eye, but with the assistance of a pocket lens the action of the tooth-ribbon is beautifully shown as it issues from its socket, makes its sweeping curve, with the tiny teeth glittering like specks of glass, and then is withdrawn ready for another sweep.