serve as rullocks for ethereal rowers to navigate this brilliant gondola." In Thames water, Navicula exist in great abundance, the most common form being that of an Indian canoe, with a gracefully curved prow.*

The flint which forms the skeleton of the diatom, and the armour of the animalcule, is withdrawn from its solution in the waters inhabited by these minute organisms by some mysterious operation of the vital force. So prolific are these tiny forms of life, that it has been estimated that a single animalcule can increase to such an extent during one month, that its entire descendants can form a bed of silica or flint twenty-five square miles in extent, and one foot and three-quarters thick! "As a parallel to Archimedes," says Bischof, "who declared he could move the earth if he had a lever long enough, we may say :-Give us a mailed animalcule, and with it we will in a short time separate all the carbonate of lime and silica from the ocean!"

This leads us to consider more minutely the part played by the animals and plants of the invisible world in the formation of the beds of rock which form the solid crust of our globe. Twenty years ago Professor Ehrenberg discovered a wonderful bed of earth which was almost entirely composed of living infusoria, and which extended to twenty, and, in some localities, even to sixty feet in depth. This formation is situated in Berlin, at a depth of

* Navicula hippocampus.

about fifteen feet below the pavement of the city. How life is sustained in this subterranean world of infusoria is a mystery, since it is evident that the organisms cannot come in contact with any air except that which is contained in the water which percolates through the mass.

This discovery was followed by others equally astounding. A mass, more than twenty feet in thickness, of light silicious earth, was found at Ebsdorf, in Hanover, and, on examination by the microscope, it appeared that this earth consisted entirely of the minute shields of invisible infusoria. Again, the beds of silicious marls upon which the towns of Richmond and Petersburg, in Virginia, are built, are now known to be almost wholly made up of the skeletons of diatomacœe. The forms that predominate are elegant saucer-shaped shields, elaborately ornamented with hexagonal spots disposed in curves, and resembling the engine-turned sculpturing on a watch. They vary in size from the one-hundredth to the one-thousandth of an inch in diameter.*

We need not carry our microscope out of England to discover the remains of infusoria in the earth's crust. The white chalk which underlies or forms the surface of the south-eastern part of England, is a mere aggregation of microscopic shell and corals, so minute that upwards of a million of the former are contained in a single cubic inch of this well* Dr. Mantell.

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known substance. These little shells, which remind us of those of the nautili, are the calcareous envelopes of the animalcules termed foraminifera, which abound in modern seas, and are constantly contributing to the amount of sediment now forming in the bed of the ocean. The beautiful white stone called calcaire grossier, which furnishes the inhabitants of Paris with a cheap and inexhaustible supply of building material, has almost the same structure as chalk; and Professor Ansted has observed that the capital of France, as well as the towns and villages of the neighbouring departments, are almost entirely built of foraminifera.

These stupendous results produced by the agency of creatures that are separately invisible to the naked eye, direct our thoughts to the Creator who has thought fit to endow these living atoms with powers that render them such important instruments in effecting the changes in the earth's surface, which His infinite wisdom has planned.

Let us quit the infusoria and glance with our microscopic eye at some other marvellous objects belonging to the invisible world. If we look through our magic tube at the downy mould formed upon any decaying substance, a wonderful forest of delicate thread-like plants will be revealed. These beautiful fungi will be seen to multiply and grow, to swell and finally to burst, scattering their invisible spores into the surrounding air.

If we make use of our microscope to examine the

eggs of insects we shall have cause to wonder at their elaborate carving and beautiful forms. It is impossible to convey to the reader an adequate idea of the elegant design and delicate sculpturing of some of these insect-eggs; few of which, be it observed, are what is commonly termed egg-shaped. It is impossible to account for the strange diversities of form in these egglets; thus, in the small and great peacock butterflies, which differ in little but size, the egg of the first is a cylinder with eight prominent ribs, while that of the latter is shaped like a Florence flask and has no ribs. Why the little peacock should escape from a barrel, and the big one from a bottle, is a problem as yet unsolved. Here are the eggs of four different members of the butterfly family. To the unaided eye they appear mere uninteresting dots, about the size of a pin's head, but if we examine them microscopically, we shall find that nature has spared no pains in decorating these minute objects. One of these eggs is an elegant turban, having a round button in the centre of the depressed crown; another is a very elaborate poundcake; the third a fairy foot ball, covered with a network of extremely minute hexagonal meshes; and the fourth is a little spherical summer-house of rustic-work roofed with flat tiles. The last simile is a little strained, as it is not easy to imagine a rustic arbour shaped like a balloon, but we must remind the reader that we meet with forms in the invisible world that cannot be likened to any object

that exists within the sphere of unaided vision. The smaller insects deposit eggs that are still more curious than those of the butterflies and moths. The egg of the lace-fly is like an unripe cherry with a long white transparent stem; that of the blowfly like a white cucumber with longitudinal stripes; and that deposited by the bug has been well compared to a circular game-pie with a standing crust, the lid of which is lifted when the young one makes its exit after hatching.

The microscope reveals many wonderful peculiarities of structure in the beings whose eggs we have just examined. The coloured dust of the butterfly's wing turns out to be feathery-scales of a tapering form, with deeply-cut notches at their broad end. The hairs of the bee are seen to be thickly beset with still finer hairs. The smallest fly is found to possess an elaborate pumping apparatus or trunk, compared with which the pumps constructed by man are clumsy and inefficient. The eyes of insects are composite, each visible eye being made up of thousands that are invisible; no less than twenty thousand of these minute organs have been detected by means of the microscope in the head of the hawk-moth. But our space is limited, and we dare not enter any further into the subject of insect anatomy.

The dust of the butterfly's wing is remarkable enough, but the fertilizing dust or pollen that covers the stamens of flowers, appears still more curious to