Darwin relates a case of this kind of passion suddenly appearing in a wild duck. The fact is related by Mr. Hewitt as follows:--“After breeding a couple of seasons with her own mallard, she at once shook him off on my placing a male pintail in the water. It was evidently a case of love at first sight, for she swam about the new-comer caressingly, though he appeared evidently alarmed and averse to her overtures of affection. From that hour she forgot her old partner. Winter passed by, and the next spring the pintail seemed to have become a convert to her blandishments, for they nested and produced seven or eight young ones.”[45] It is difficult not to attribute such deviations as these to motives similar to those by which we are ourselves actuated--to passion, caprice, or depravity. They certainly cannot be accounted for by the theory of mechanical and immutable instinct. Such facts clearly prove that animal psychology, although less complicated than our own, does not differ essentially from it, and consequently throws much light on our present investigation. The adventure of the wild duck, for example, may, without any alteration, be read as a human adventure, proving for the hundred-thousandth time that the heart, or what we call by that name, is versatile; that conjugal fidelity does not always resist a strong impression arising from a chance encounter; that novelty has a disturbing effect; and, finally, that indifference and coldness can rarely hold out against the persistent advances of one who loves ardently enough not to yield to discouragement. Dante has already made this last reflection in his celebrated line-- “Amor ch’a nullo amato amar perdona.” To quote Dante _à propos_ of the illicit amours of a pintail and a wild duck may shock the learned, but the aptness of the quotation proves once more the essential identity of the animal and human organisms. III. _The Family amongst Animals._ If the study of the modes of sexual union amongst animals is not useless to the sociologist, that of the animal family is at least quite as interesting. This latter confirms the inductions of theorists relative to the primitive form of the human family. The animal family is especially maternal. The female of birds, immediately she has laid her eggs, experiences a sort of intoxication; to sit becomes for her an imperious need, which completely transforms her moral nature. In January 1871, during the bombardment of Paris, a German shell, bursting in the loft of a house inhabited by one of my friends, was powerless to disturb a female pigeon absolutely enchained by the passion of incubation. It is amongst birds that the animal family is best constituted; this, however, differs much according to the species, especially as regards the participation of the male in the rearing of the young.