Popular imagination prefers the clear and concrete; it does not recognize any abstract laws that rule the universe. Nothing exists without a cause, but this cause is not sought in an agglomeration of external or internal forces; it is taken to be simple and palpable, a personal being, a god or a king. Is it not natural, then, that marriage, which plays such an important part in the life of the individual, as well as in that of the people, should be ascribed to a wise and powerful ruler, or to direct divine intervention? With notions of this kind science has nothing to do. If we want to find out the origin of marriage, we have to strike into another path, the only one which can lead to the truth, but a path which is open to him alone who regards organic nature as one continued chain, the last and most perfect link of which is man. For we can no more stop within the limits of our own species, when trying to find the root of our psychical and social life, than we can understand the physical condition of the human race without taking into consideration that of the lower animals. I must, therefore, beg the reader to follow me into a domain which many may consider out of the way, but which we must, of necessity, explore in order to discover what we seek. It is obvious that the preservation of the progeny of the lowest animals depends mainly upon chance. In the great sub-kingdom of the Invertebrata, even the mothers are exempted from nearly all anxiety as regards their offspring. In the highest order, the Insects, the eggs are hatched by the heat of the sun, and the mother, in most cases, does not even see her young. Her care is generally limited to seeking out an appropriate place for laying the eggs, and to fastening them to some proper object and covering them, if this be necessary for their preservation. Again, to the male’s share nothing falls but the function of propagation.[13] In the lowest classes of the Vertebrata, parental care is likewise almost unheard of. In the immense majority of species, young fishes are hatched without the assistance of their parents, and have, from the outset, to help themselves. Many Teleostei form, however, an exception; and, curiously enough, it is the male on which, in these cases, the parental duty generally devolves. In some instances he constructs a nest, and jealously guards the ova deposited in it by the female; while the male of certain species of Arius carries the ova about with him in his capacious pharynx.[14] Most of the Reptiles place their eggs in a convenient and sunny spot between moss and leaves, and take no further trouble about them. But several of the larger serpents have a curious fashion of laying them in a heap, and then coiling themselves around them in a great hollow cone.[15] And female Crocodiles, as also certain aquatic snakes of Cochin China, observed by Dr. Morice, carry with them even their young.[16]