These classes are selected, in obedience to necessary limitations, as representing the twelve chief labours of man which have given shape to the majority of his haunting demons, as distinguished from his devils. Of course all classifications of this character must be understood as made for convenience, and the divisions are not to be too sharply taken. What Plotinus said of the gods, that each contained all the rest, is equally true of both demons and devils. The demons of Hunger are closely related to the demons of Fire: Agni devoured his parents (two sticks consumed by the flame they produce); and from them we pass easily to elemental demons, like the lightning, or demons of fever. And similarly we find a relationship between other destructive forces. Nevertheless, the distinctions drawn are not fanciful, but exist in clear and unmistakable beliefs as to the special dispositions and employments of demons; and as we are not engaged in dealing with natural phenomena, but with superstitions concerning them, the only necessity of this classification is that it shall not be arbitrary, but shall really simplify the immense mass of facts which the student of Demonology has to encounter. But there are several points which require especial attention as preliminary to a consideration of these various classes of demons. First, it is to be borne in mind that a single demonic form will often appear in various functions, and that these must not be confused. The serpent may represent the lightning, or the coil of the whirlwind, or fatal venom; the earthquake may represent a swallowing Hunger-demon, or the rage of a chained giant. The separate functions must not be lost sight of because sometimes traceable to a single form, nor their practical character suffer disguise through their fair euphemistic or mythological names.