As to the corresponding articles in Nature, they are very numerous. We will take, for example, the Saddle-back or Crow Oyster of our own shores. It is a most remarkable being. It deposits upon the object to which it adheres a sort of button of shelly matter, and the lower valve, which is nearly flat, has in it an aperture which is placed over the knob, just as a button-hole goes over the button. As this arrangement is confined to the lower valve, and cannot be seen unless the upper valve be removed, the lower valve only is shown in the illustration, as it appears when fastened to the side of a large limpet.
Of the Hooks and Eyes in Nature I have only taken two examples, though there are many others.
We all know the Bees, Wasps, Hornets, and other similar insects, and that they possess four wings. I may here mention that no insect which does not possess four transparent wings is capable of stinging.
When the insect is at rest the four wings may be easily distinguished, but when it is in flight they coalesce, so that practically the insect has two wings instead of four. This object is attained in the following way:—
The lower edge of the first pair of wings is turned over in a rather stiff fold. The upper edge of the second pair of wings has a row of small, but strong and elastic hooks. When the insect is about to fly, the hooks are hitched into the fold, and so the wings are fastened together. These hooks are shown in the illustration, and the reader will easily see how effective they must be in their operation. An almost exactly similar structure is found in the feathers of birds, and it is by means of these tiny hooks that wings are enabled to present a continuous, light, and elastic surface in the air.
USEFUL ARTS.
CHAPTER IV.
THE STOPPER, OR CORK.—THE FILTER.
Vessels and their Covers.—Corks.—Mode of bottling Wine.—Conical Corks and Stoppers.—Self-fitting Candles.—Candle-fixers.—The Vent-peg.—The Blow-guns and their Missiles.—The Serpula and its Conical Stopper.—The Filter.—The Bosjesman procuring Water.—How to make a simple Filter.—The Earth as a Filter.—The Sea-mouse, or Aphrodite, and its filtering Apparatus.—The Duck’s Beak, and its beautiful Structure.—The Jaw of the Greenland Whale.—Fork-grinder’s Respirator.—How Insects breathe.—Spiracles, and their general Structure.—Spiracle of the Fly.—Experiment upon a Cockroach, and its Result.
The Stopper, or Cork.
THIS object, as depicted in the illustration, is a product of civilised life, though, as soon as a savage could make a vessel, he seems to have made a Cover for it if it were of large diameter, or a Stopper if the opening were small. Even the very Bosjesman, who is quite unable to make a clay vessel, and uses empty ostrich eggs by way of water-bottles, is yet capable of making plugs with which he can stop up the apertures. Then the Kafir, with his gourd vessels, whether they be for water or snuff, makes a plug that fits tightly enough to exclude the air, as well as to retain the contents.