περὶ ψυχῆς. _On soul._ περὶ αἰσθήσεως καὶ αἰσθητῶν. _On sense and objects of sense._ περὶ ζωῆς καὶ θανάτου. _On life and death._ περὶ μνήμης καὶ ἀναμνήσεως. _On memory and reminiscence._ περὶ ὓπνου καὶ ἐγρηγόρσεως. _On sleep and waking._ περὶ ἐνυπνίων. _On dreams._ [προβλήματα. _Problems._] [περὶ χρωμάτων. _On colours._] [περὶ ἀκουστῶν. _On sounds._] [περὶ τῆς καθ’ ὔπνον μαντικῆς. _On prophecy in sleep._] Of these works some, the names of which are placed here in brackets, are clearly spurious in that they were neither written by Aristotle nor are they in any form approaching that in which they were cast by him. Yet all are of very considerable antiquity and contain fragments of his tradition in a state of greater or less corruption. In addition to works here enumerated there are many others which are spurious in a yet further sense in that they are merely fathered on Aristotle and contain no trace of his spirit or method. Such, for example, is the famous mediaeval work of oriental origin known as the _Epistle of Aristotle to Alexander_. In a general way it may be stated that the _physical_ works, with which we are not here directly concerned, while they show ingenuity, learning, and philosophical power, yet betray very little direct and original observation. They have exerted enormous influence in the past and for at least two thousand years provided the usual physical conceptions of the civilized world both East and West. After the Galilean revolution in physics, however, they became less regarded and they are not now highly esteemed by men of science. The _biological_ works of Aristotle, on the other hand, excited comparatively little interest during the Middle Ages, but from the sixteenth century on they have been very closely studied by naturalists. From the beginning of the nineteenth century, and especially as a result of the work of Cuvier, Richard Owen, and Johannes Müller, Aristotle’s reputation as a naturalist has risen steadily, and he is now universally admitted to have been one of the very greatest investigators of living nature.