From this drop of water you may draw inferences and conclusions respecting the entire mass of waters which occupy the basins of the seas, and form three-fourths of the surface of our globe. In order that some conception may be reached of the enormous numbers of the living beings contained in the seas now, and formerly, we may fitly recall in this place a fact well known to geologists. It is, that all building stone, all the calcareous earth of which chalk hills and banks are formed, are entirely composed of the pulverized and agglomerated remains of the shells of mollusca, visible or microscopic, which, in the most remote ages of the existence of the globe, peopled the basin of the seas. The whole of this formation is composed of the accumulation of shells. If life has been lavished with such profusion in the waters during the geological periods, it must be equally lavished now, in almost similar ways, because the actual conditions of nature do not differ from what they were in the primitive ages of the globe. The air which surrounds us is, like the earth and the seas, a vast receptacle of living creatures. We see only a few animals cleaving the aërial space, but the _savant_, who looks beyond the simple appearance of things, discovers myriads of existences in the air. The air seems to us very pure, very transparent, but only because it is not sufficiently illumined by light to enable us to perceive the particles, or foreign bodies, which are floating about in it. When we allow one ray of daylight to penetrate into a closed room, one thread of solar light, we can discern a luminous streak flung across the chamber, while the remaining portion is still in darkness. We all know that, thanks to the powerful light, and its contrast with the surrounding obscurity, the luminous streak is seen to be filled with light, slender floating bodies, rising, descending, fluttering with the motion of the air. That which is perceptible in the atmosphere of a brightly-lighted room is necessarily existent in the entire atmosphere surrounding our globe, so that the air is everywhere filled with these specks of dust. Of what are these specks of dust formed? Almost entirely of living creatures, of the germs of microscopic plants (cryptogamia), or of the eggs of inferior animals (zoophytes). So-called spontaneous generation, so largely discussed of late in France and other countries, is merely due to these organic germs which fill the atmosphere, and which, falling into the water, or into the infusions of plants, give birth to forms of vegetation, which have been imputed to spontaneous generation; that is to say, to a creation without a germ, a generation without a cause, which is an error. Every living thing has parents, which are always discoverable by science and attention.