Hypotheses as to the periodicity in the sexual life of animals, p. 25.—Every month or season of the year the pairing season of one or another mammalian species, pp. 25, _et seq._—The rut not dependent upon any general physiological law, but adapted to the requirement of each species separately, pp. 26, _et seq._—Wild species without a definite pairing season, p. 27.—Rutting season among the man-like apes, _ibid._—Among our earliest human or half-human progenitors, p. 28.—Periodical increase of the sexual instinct among existing savages, pp. 28-31.—Among civilized peoples, pp. 31-33.— The increase of the sexual instinct at the end of spring or in the beginning of summer, probably a survival of an ancient pairing season, pp. 34, _et seq._—The winter maximum of conceptions, pp. 35-37.—Why man is not limited to a particular period of the year in which to court the female, pp. 37, _et seq._—Domestic animals without a definite pairing season, p. 38. CHAPTER III THE ANTIQUITY OF HUMAN MARRIAGE Marriage a necessary requirement for the existence of the human race, p. 39.—The hypothesis that the maternal uncle was the guardian of the children, pp. 39-41.—The father the head of the family, p. 41.—The hypothesis that all the men of the tribe indiscriminately were their guardians, pp. 41, _et seq._—Man originally not a gregarious animal, pp. 42, _et seq._—The solitary life of the man-like apes, _ibid._—Savage peoples living in families rather than in tribes, pp. 43-47.—Insufficient food supply a hindrance to a true gregarious manner of living, pp. 47-49.—The gregariousness and sociability of man sprang in the main from progressive intellectual and material civilization, pp. 49, _et seq._ CHAPTER IV A CRITICISM OF THE HYPOTHESIS OF PROMISCUITY