two lenses placed at a distance, so that the one next the eye magnifies the enlarged image of any object placed in front of the other, was invented by a spectacle-maker at Middleburg, in Holland, about the year 1590. This Dutch microscope, rudely formed of two lenses and a wooden tube, was the germ of the beautiful and complex instrument of modern times. Let us now peep through this wondrous spy-glass into the invisible world.
In a single drop of stagnant water we may discover a world of marvellous creatures, whose eccentric forms baffle description. In some of these tiny monsters it is not easy to detect any definite shape, as their bodies are destitute of any solid support, and seem to be composed of gelatinous matter, which may take almost any figure. In others, there is still a considerable variety in the forms assumed by the same individual under different circumstances, but the prevailing shape can be recognised. In others, again, the body, although still unprotected by any firm envelope, appears to undergo little change in figure, except when affected by temporary pressure. But there are many that cannot be influenced even by pressure, their soft bodies being inclosed in coats of flinty mail. All these creatures move about in the water with great rapidity, yet they have neither arms, legs, nor fins. Their movements are performed by means of peculiar processes called cilia, which resemble minute hairs. So active are these cilia, and such restless
