Not only did our mediaeval ancestors believe all sorts of fancies as to the propagation of lower animals and plants, but they were quite prepared to accept stories as to reproduction in the case of higher animals, and even in mankind, by irregular methods, such as parthenogenesis, or the defect of an ordinary male parent. In the Middle Ages in Europe, and earlier in the East, the belief in the frequent occurrence of the birth of a child which had no human male parent was common. It was, so to speak, an admitted though irregular occurrence. A very curious thing is that when such cases were supposed to occur, they were not ascribed to any natural process such as we now recognise in the "parthenogenesis" of insects and crustaceans, but to the visitation of the mother by a spirit--a floating, volatile demon or angel (known as an "incubus" in the Middle Ages) beneficent or malicious as the case might be. Stories of the nocturnal visits of these mysterious ghostly "incubi" are on record in great number and variety, both in European and Oriental tradition and legend. There seems to have been a readiness to believe the theory of paternity from among the hidden world of goblins, fairies, and sprites which was very naturally made use of by a woman and her relatives when she could not produce the father of her child. We come across examples of such beliefs in invisible agents of paternity even among the more cultivated Romans. Thus Virgil in his "Georgics" cites as a fact that mares are fertilised by the wind. His words are given on the next page.