Within the limits of Greek folk-lore we have already once encountered such a belief, namely in the case of the ‘Striges,’ old witches capable of turning themselves into birds of prey; and in the folk-lore of the world at large the idea is extremely frequent. There is no need to encumber this chapter with a mass of recorded instances; the verdict of the first authority on the subject is sufficient. According to Tylor[652], the belief ‘that certain men, by natural gift or magic art, can turn for a time into ravening wild beasts’ is ‘a widespread belief, extending through savage, barbaric, classic, oriental, and mediaeval life, and surviving to this day in European superstition.’ ‘The origin of this idea,’ he says, ‘is by no means sufficiently explained,’ but he notes that ‘it really occurs that, in various forms of mental disease, patients prowl shyly, long to bite and destroy mankind, and even fancy themselves transformed into wild beasts.’ Whether such cases of insanity are the cause or the effect of the belief, he does not determine; but he adds, what is most important to the present issue, that ‘professional sorcerers have taken up the idea, as they do any morbid delusion, and pretend to turn themselves and others into beasts by magic art’; and, later on[653], citing by way of illustration a passage of the _Eclogues_[654], in which Vergil ‘tells of Moeris as turning into a wolf by the use of poisonous herbs, as calling up souls from the tombs, and as bewitching away crops,’ he points out that in the popular opinion of Vergil’s age ‘the arts of the werewolf, the necromancer or “medium,” and the witch, were different branches of one craft.’ If then the Centaurs were a tribe of reputed sorcerers and also obtained the secondary name of ‘Beasts,’ the analogy of worldwide superstitions suggests that the link between these two facts is to be found in their magical power of assuming the shape of beasts.