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it issues from its socket, makes its sweeping curve, with the tiny teeth glittering like specks of glass, and then is withdrawn ready for another sweep. Should sea-water and living Periwinkles not be easily obtained, the same phenomenon may be observed in fresh water, and with the common Pond-snail, which may be caught by thousands in any stream and in most ponds. THE CIRCULAR SAW. In one sense the Cordon Saw is a Circular Saw, but we now restrict the name to the tool which has a circular blade, more or less deeply toothed on the edge. The largest and coarsest of these saws are of enormous diameter, have teeth several inches in length, and can cut a large tree-trunk asunder in a wonderfully short time.