So far, therefore, there seems to be a complete parallelism between the evolution of animal and vegetable life from the earliest to the latest, and from the simplest to the most complex forms. These facts point strongly to a process of evolution by which the animal and vegetable worlds, starting from a common origin in protoplasm, the lowest and simplest form of living matter, have gradually advanced step by step, along diverging lines, until we have at last arrived at the sharp antithesis of the ox and the oak tree. It is clear, however, that this evolution has gone on under what I have called the generalised law of polarity, by which contrasts are produced of apparently opposite and antagonistic qualities, which however are indispensable for each other’s existence. Thus animals could not exist without plants to work up the crude inorganic materials into the complex and mobile molecules of protoplasm, which are alone suited for assimilation by the more delicate and complex organisation of animal life. Plants, on the other hand, could not exist without a supply of the carbonic dioxide, which is their principal food, and which animals are continually pouring into the air from the combustion of their carbonised food in oxygen, which supplies them with heat and energy. Thus nature is one huge aquarium, in which animal and vegetable life balance each other by their contrasted and supplemental action, and, as in the inorganic world, harmonious existence becomes possible by this due balance of opposing factors. CHAPTER VIII. PRIMITIVE POLARITIES—POLARITY OF SEX. Sexual generation—Base of ancient cosmogonies—Propagation non-sexual in simpler forms—Amœba and cells—Germs and buds—Anemones—Worms—Spores—Origin of sex—Ovary and male organ—Hermaphrodites—Parthenogenesis—Bees and insects—Man and woman—Characters of each sex—Woman’s position—Improved by civilisation—Christianity the feminine pole—Monogamy the law of nature—Tone respecting women test of character—Women in literature—In society—Attraction and repulsion of sexes—Like attracts unlike—Ideal marriage—Woman’s rights and modern legislation.