Thus on the whole we are concerned in these volumes with the reverence or worship paid by men to the natural resources from which they draw their nutriment, both vegetable and animal. That they should invest these resources with an atmosphere of wonder and awe, often indeed with a halo of divinity, is no matter for surprise. The circle of human knowledge, illuminated by the pale cold light of reason, is so infinitesimally small, the dark regions of human ignorance which lie beyond that luminous ring are so immeasurably vast, that imagination is fain to step up to the border line and send the warm, richly coloured beams of her fairy lantern streaming out into the darkness; and so, peering into the gloom, she is apt to mistake the shadowy reflections of her own figure for real beings moving in the abyss. In short, few men are sensible of the sharp line that divides the known from the unknown; to most men it is a hazy borderland where perception and conception melt indissolubly into one. Hence to the savage the ghosts of dead animals and men, with which his imagination peoples the void, are hardly less real than the solid shapes which the living animals and men present to his senses; and his thoughts and activities are nearly as much absorbed by the one as by the other. Of him it may be said with perhaps even greater truth than of his civilised brother, “What shadows we are, and what shadows we pursue!” But having said so much in this book of the misty glory which the human imagination sheds round the hard material realities of the food supply, I am unwilling to leave my readers under the impression, natural but erroneous, that man has created most of his gods out of his belly. That is not so, at least that is not my reading of the history of religion. Among the visible, tangible, perceptible elements by which he is surrounded—and it is only of these that I presume to speak—there are others than the merely nutritious which have exerted a powerful influence in touching his imagination and stimulating his energies, and so have contributed to build up the complex fabric of religion. To the preservation of the species the reproductive faculties are no less essential than the nutritive; and with them we enter on a very different sphere of thought and feeling, to wit, the relation of the sexes to each other, with all the depths of tenderness and all the intricate problems which that mysterious relation involves. The study of the various forms, some gross and palpable, some subtle and elusive, in which the sexual instinct has moulded the religious consciousness of our race, is one of the most interesting, as it is one of the most difficult and delicate tasks, which await the future historian of religion.