There is nothing surprising to the naturalist in this procreative explosion, which evolves altruism out of egotism. We know too well, however, that it has not appeared so simple a matter to many philosophers and celebrated literary men, little familiar with biological sciences. A belated metaphysician, Schopenhauer, who has lately become fashionable, adopting the ancient stereotyped doctrine which makes Nature an anthropomorphic personage, has gratuitously credited her with quite a profound diplomatic design. According to him, it is a foregone conclusion that she should intoxicate individuals with love, and thus urge them on, without their suspecting it, to sacrifice themselves to the major interest of the preservation of the species. The glance that we have just thrown on the processes of reproduction, from the paramœcium up to man, suffices to refute this dream. I will not, however, dwell on this. What is here of great interest is to inquire how the superior animals comport themselves when pricked by desire, and to note the principal traits of their sexual psychology; for here again we shall have to recognise more than one analogy to what happens in regard to man; and we shall also see later that there exists both in the animal and the man some relation between the manner in which sexual attraction is felt and the greater or less aptitude for durable pairing, and consequently for marriage and the family. Without giving more time than is necessary to these short excursions into animal psychology, it will be well to pause on them for a moment. They throw a light on the sources of human sociology; they force us also to break once for all with the abstract and trite theories which have inspired, on the subject of marriage and the family, so much empty writing and so many satiating trivialities. It is in animality that humanity has its root; it is there, consequently, that we must seek the origins of human sociology. IV. _Loves of Animals._