XIV. ‘However, if we are at last to have done with notions enslaved to usage,[328] and to state fearlessly what appears to be true, it is probable that no part of a whole has any order, or position, or movement of its own which can be described in absolute terms as natural. But when each body places itself at the disposal of that on account of which it has come into being, [Sidenote: E] and in relation to which it naturally exists or has been created, to move as is useful and convenient to it, actively and passively and in all its own states conforming to the conservation, beauty, or power of that other, then, I hold, its place, movements and disposition are according to Nature. In man certainly, who has, if anything has, come into being according to Nature, [Sidenote: F] the heavy and earth-like parts are found above, mostly about the head, the hot and fiery in the middle regions; of the teeth one set grows from above, the other from below, yet neither contrary to Nature; nor can it be said of the fire in him that when it is above and flashes in his eyes it is natural, but when it is in stomach or heart, unnatural; each has been arranged as is proper and convenient. _Mark well the tortoise and the trumpet-shell_, says Empedocles, and, we may add, the nature of every shell-fish, and _Earth uppermost, flesh under thou shalt see._ Yet the stony substance does not squeeze or crush the growth[329] [Sidenote: 928] within, nor again does the heat fly off and be lost because of its lightness; they are mingled and co-ordinated according to the nature of each.