The old idea of spontaneous generation is now taken in many different senses. It is owing to this indistinctness of the idea, and its application to so many different hypotheses, that the problem is one of the most contentious and confused of the science of the day. I restrict the idea of spontaneous generation--also called abiogenesis or archigony--to the first development of living protoplasm out of inorganic carbonates, and distinguish two phases in this "beginning of biogenesis": (1) _autogony_, or the rise of the simplest protoplasmic substances in a formative fluid, and (2) _plasmogony_, the differentiation of individual primitive organisms out of these protoplasmic compounds, in the form of _monera_. I have treated this important, though difficult, problem so exhaustively in the fifteenth chapter of my _Natural History of Creation_ that I may content myself here with referring to it. There is also a very searching and severely scientific inquiry into it in my _General Morphology_ (1866). Naegeli has also treated the hypothesis in quite the same sense in his mechanico-physiological theory of descent (1884), and has represented it to be an indispensable thesis in any natural theory of evolution. I entirely agree with his assertion that "to reject abiogenesis is to admit a miracle." The hypothesis of spontaneous generation and the allied carbon-theory are of great importance in deciding the long-standing conflict between the _teleological_ (dualistic) and the _mechanical_ (monistic) interpretation of phenomena. Since Darwin gave us the key to the monistic explanation of organization in his theory of selection forty years ago, it has become possible for us to trace the splendid variety of orderly tendencies of the organic world to mechanical, natural causes, just as we could formerly in the inorganic world alone. Hence the supernatural and telic forces, to which the scientist had had recourse, have been rendered superfluous. Modern metaphysics, however, continues to regard the latter as indispensable and the former as inadequate.