On the other hand, the analysis of the movements of several stars, such as Sirius, Procyon, Altair, and many others, proves that these far-distant suns have companion planets as yet unrevealed by the telescope, and which possibly may never be discovered because they are dark and lost in the radiation of the star. The companion discovered in the neighbourhood of Sirius is not the only celestial body of that system. Scheiner speaks of about 10 million stars as constituting the sidereal universe. But the photographic chart of the heavens which comprises stars down to the thirteenth magnitude is already expected to contain 30 millions. If we go down to the lowest magnitudes we reach the figure of 100 millions. It is therefore not an army of 100,000 worlds which appears before us, but rather of several millions. Now, this is a point of the greatest importance for the exact appreciation of the problem. The terrestrial organisms from the lowest up to man are the result of forces in action on the surface of our planet. The first organisms seem to have been produced by combinations of carbon with hydrogen and oxygen, and their life consisted, so to speak, only in a few rudimentary sensibilities. Sponges, corals, polypi, medusæ, give us an idea of these primitive beings. They were formed in the warm waters of the primary ages. While there were yet no continents nor islands emerging from the universal ocean, there were no air-breathing organisms. The first aquatic beings were succeeded by amphibia and reptiles. Afterwards came the mammalia and the birds. The constitution of beings stands in close relation with the substances of which they are composed, the medium in which they live, the temperature, the light, the density, gravitation, length of day and night, seasons, etc.--in a word, all the cosmographic elements of the planet.