Soon after the powers of the microscope became known, these Wheel-bearers were discovered, and for a long time they were thought to have a pair of veritable revolving wheels upon their heads. They were naturally held in high estimation, as, although almost every kind of lever can be found in the animal world, a revolving wheel had never been seen. However, as the defining powers of the microscope improved, the so-called wheels were found not to be wheels at all, but stationary organs, and that their apparent revolution was nothing but an optical delusion.
The wheels are, in fact, two discs, around the edges of which are set certain hair-like appendages, called “cilia,” from a Latin word signifying the eyelashes. Each of the cilia has an independent motion of its own, and, as they bend in rapid and regular succession, they produce an effect on the eye similar to that of a revolving body. As for the animal itself, they produce a double effect, either acting as paddles, and forcing the animal through the water, or, when it is affixed to some object, causing a current which drives into its mouth the minute beings on which it feeds.
The particular species of Wheel-hearer whose mouth is here shown is called scientifically Limnias ceratophylli. It derives the latter name from the fact that it is mostly found on the submerged stems and leaves of the Hornwort (Ceratophyllum), which is very common in ponds and slow streams. The creature is, however, to be found on the water-growing plants, and Mr. Gosse, in his “Evenings with the Microscope,” gives a very full and graphic account of itself and its habits.
He specially mentions the use of the wheels, and, by dissolving a little carmine in the water, had the pleasure of seeing the coloured granules swept into the mouth by the current caused by the cilia through the jaws, and so into the stomach.
USEFUL ARTS.
CHAPTER I.
PRIMITIVE MAN AND HIS NEEDS.—EARTHENWARE.—BALL-AND-SOCKET JOINT.—TOGGLE OR KNEE JOINT.
Contrast between Savagery and Civilisation.—Manufacture of Weapons.—Earthenware of Art.—Sun-baked Vessels.—Earthenware of Nature.—Nest of Pied Grallina.—Analogy with the Babylonish Brick.—Nest of the Oven-bird.—A partitioned Vessel.—Necked earthenware Vessels.—Nests of Eumenes, Trypoxylon, and Pelopœus.—Proof of Reason in Insects.—The Ball-and-socket Joint.—“Bull’s-eye” of Microscope.—The human Thigh-bone.—Vertebræ of the Serpents and their Structure.—The Sea-urchin and its Spines.—Legs and Antennæ of Insects.—The Toggle or Knee Joint, and its Use in the Arts.—The hand Printing-press and the Toggle-joint.—The human Leg and Arm.—Power of the natural Toggle-joint.—Fencing and Boxing.—Heads of Carriages.—“Bowsing” of Ropes.—Leaf-rolling Caterpillars.
IN the primitive ages of Man the aids to civilisation were very few and very rude. Some of them, especially those which relate to hunting and war, have already been mentioned, and we now have to deal with some of those which bear upon domestic life.
Here we are in some little difficulty, for it is not very easy to draw the line where domestic life begins, or the mode in which it shall be defined. We may at all events connect domestic life with a residence of some sort, and may, in consequence, neglect all such primitive savages as need no domestic implements.
Such, for example, are the few surviving Bosjesmans of Southern Africa, not one of whom ever made a tool or an implement, or looked beyond the present day. The genuine Bosjesman can make a bow and poison his arrows, and he can light a fire; but there his civilisation ends. He cannot look beyond the present hour, he has not the faintest notion of making a provision for the future, nor did his wildest imagination ever compass the idea of a pot or a pan.
He kills his prey, and, if hunger be very pressing, he will eat it at once without waiting for the tedious ceremony of cooking; or at the best will just throw the meat upon the fire, tear it to pieces with his teeth, and swallow it when it is nothing but a mass of bleeding flesh, charred on the outside, and absolutely raw within. The Bosjesman has not even a tent which he can call his own, any bush or hole in the ground answering for a house as long as he wants it, and then being exchanged for another.