All the different philosophical tendencies may, from the point of view of modern science, be ranged in two antagonistic groups; they represent either a _dualistic_ or a _monistic_ interpretation of the cosmos. The former is usually bound up with teleological and idealistic dogmas, the latter with mechanical and realistic theories. Dualism, in the widest sense, breaks up the universe into two entirely distinct substances--the material world and an immaterial God, who is represented to be its creator, sustainer, and ruler. Monism, on the contrary (likewise taken in its widest sense), recognizes one sole substance in the universe, which is at once "God and nature"; body and spirit (or matter and energy) it holds to be inseparable. The extramundane God of dualism leads necessarily to theism; and the intra-mundane God of the monist leads to pantheism. The different ideas of _monism_ and _materialism_, and likewise the essentially distinct tendencies of theoretical and practical materialism, are still very frequently confused. As this and other similar cases of confusion of ideas are very prejudicial, and give rise to innumerable errors, we shall make the following brief observations, in order to prevent misunderstanding: I. Pure monism is identical neither with the theoretical materialism that denies the existence of spirit, and dissolves the world into a heap of dead atoms, nor with the theoretical spiritualism (lately entitled "energetic" spiritualism by Ostwald) which rejects the notion of matter, and considers the world to be a specially arranged group of "energies" or immaterial natural forces. II. On the contrary, we hold, with Goethe, that "matter cannot exist and be operative without spirit, nor spirit without matter." We adhere firmly to the pure, unequivocal monism of Spinoza: Matter, or infinitely extended substance, and spirit (or energy), or sensitive and thinking substance, are the two fundamental attributes or principal properties of the all-embracing divine essence of the world, the universal substance. (Cf. chap. xii.) CHAPTER II OUR BODILY FRAME Fundamental Importance of Anatomy--Human Anatomy--Hippocrates, Aristotle, Galen, Vesalius--Comparative Anatomy--Georges Cuvier--Johannes Müller--Karl Gegenbaur--Histology--The Cellular Theory--Schleiden and Schwann--Kölliker--Virchow--Man a Vertebrate, a Tetrapod, a Mammal, a Placental, a Primate--Prosimiæ and Simiæ--The Catarrhinæ--Papiomorphic and Anthropomorphic Apes--Essential Likeness of Man and the Ape in Corporal Structure