I. It is very probable that a similar biogenetic process to that of our own earth is taking place on some of the other planets of our solar system (Mars and Venus), and on many planets of other solar systems; first simple monera are formed by spontaneous generation, and from these arise unicellular protists (first plasmodomous primitive plants, and then plasmophagous primitive animals). II. It is very probable that from these unicellular protists arise, in the further course of evolution, first social cell-communities (coenobia), and subsequently tissue-forming plants and animals (metaphyta and metazoa). III. It is also very probable that thallophyta (algæ and fungi) were the first to appear in the plant-kingdom, then diaphyta (mosses and ferns), finally anthophyta (gymnosperm and angiosperm flowering plants). IV. It is equally probable that the biogenetic process took a similar course in the animal kingdom--that from the blastæads (catallacta) first gastræads were formed, and from these lower animal forms (coelenteria) higher organisms (coelomaria) were afterwards evolved. V. On the other hand, it is very questionable whether the different stems of these higher animals (and those of the higher plants as well) run through the same course of development on other planets as on our earth. VI. In particular, it is wholly uncertain whether there are vertebrates on other planets, and whether, in the course of their phyletic development, taking millions of years, mammals are formed as on earth, reaching their highest point in the formation of man; in such an event, millions of changes would have to be just the same in both cases. VII. It is much more probable, on the contrary, that other planets have produced other types of the higher plants and animals, which are unknown on our earth; perhaps from some higher animal stem, which is superior to the vertebrate in formation, higher beings have arisen who far transcend us earthly men in intelligence. VIII. The possibility of our ever entering into direct communication with such inhabitants of other planets seems to be excluded by the immense distance of our earth from the other heavenly bodies, and the absence of the requisite atmosphere in the intervening space, which contains only ether.