We have seen in the first part of our work how the speculations of those who formerly discussed the habitability of the planets not only raised the question whether such and such a planet was inhabited, but also tackled the much vaster problem of the particular characters of the beings which lived there. After attentively following the discussion, nobody should ask to penetrate further into this question. It has indeed been a great effort to obtain a positive result at all, even while restricting the population of the planets to the simplest forms of organised matter. The number of forms under which it shows itself on the Earth is so considerable that we can only be dazed by its abundance, and this impression must be even increased if we remember that the possible forms are far from being exhausted and that we only know those which, satisfying terrestrial conditions, have been able to survive by adapting themselves to their surroundings. We do not exaggerate in declaring that Nature recognises no limit to the number of forms which can harbour life, and this observation is an argument in favour of those who desire to find reasonable or superior beings in distant worlds. It indicates that as soon as the first germs of life exist, the possibility of a complete development is there, and that however different the external conditions may be, Nature is not at a loss for varieties of forms of life. That is why we have the right to hope that on Mars, for instance, there are beings who not only show manifestations of animal life, but who are endowed with intellectual faculties. That, however, is all we can acknowledge: the right to hope and not to a certainty. Yet at the risk of exposing ourselves to a criticism similar to that which we have in the first part directed against other authors, we would now invite the reader to follow us for a moment into the domain of speculation and hypothesis. THE POSSIBILITY OF BEINGS OF DIFFERENT CHEMICAL CONSTITUTION In this chapter Scheiner develops the idea indicated above (page 127) on the possibility of the existence in other worlds of living beings entirely different from ourselves.