The monistic conviction, which we thus arrived at, of the physical and chemical unity of the entire cosmos is certainly one of the most valuable general truths which we owe to astrophysics, the new branch of astronomy which is honorably associated with the name of Friedrich Zöllner. Not less important is the clear knowledge we have obtained that the same laws of mechanical development that we have on the earth rule throughout the infinite universe. A vast, all-embracing metamorphosis goes on continuously in all parts of the universe, just as it is found in the geological history of the earth; it can be traced in the evolution of its living inhabitants as surely as in the history of peoples or in the life of each human individual. In one part of space we perceive, with the aid of our best telescopes, vast nebulæ of glowing, infinitely attenuated gas; we see in them the embryos of heavenly bodies, billions of miles away, in the first stage of their development. In some of these "stellar embryos" the chemical elements do not seem to be differentiated yet, but still buried in the homogeneous primitive matter (_prothyl_) at an enormous temperature (calculated to run into millions of degrees); it is possible that the original basic "substance" (_vide_ p. 229) is not yet divided into ponderable and imponderable matter. In other parts of space we find stars that have cooled down into glowing fluid, and yet others that are cold and rigid; we can tell their stage of evolution approximately by their color. We find stars that are surrounded with rings and moons like Saturn; and we recognize in the luminous ring of the nebula the embryo of a new moon, which has detached itself from the mother-planet, just as the planet was released from the sun.