What led Aristotle to so lofty a flight of speculation? He does not tell. One may guess, however, that it may well have been this: that he had found himself obliged not only to deny the identity of the generative heat of the semen with elemental fire, but also to deny the identity with elemental fire even of the glowing sun, as well as of the other planets and the fixed stars; and to maintain that all the heavenly bodies consist of ether. These denials we have read already; they shall presently be commented on. Taking them for granted: now, since the life-giving sun is not elemental fire but ether, would not the life-giving seminal heat, which also is not elemental fire, naturally be the analogue of the ether? "Man and the sun generate man," said Aristotle, in a famous passage.[338] He needed no knowledge of chlorophyll to teach him this. The ether is the element of the sun, moon, stars, and spheres; of it consist the bodies associated with the souls of the living, unalterable, immortal, divine existences of the eternal heaven. To associate a body analogous to this ether with the dormant soul of a living existence--a living existence alterable and mortal as an individual, but one of an immortal race--in the medium which shall maintain that racial immortality by begetting a new individual out of the lower elements--this is a stroke characteristic of the man who declared that "the race of men, and of animals, and of plants, exists forever";[339] the man who assigned to every bloodless animal an analogue of the blood and an analogue of the heart,[340] to the octopus, an analogue of the brain;[341] the man in whose eyes the heavenly bodies were divine living existences running eternal courses and so, we may presume, were analogous in some degree to the living existences of the earth.[342] Harvey in one of the earlier Exercises of his treatise On Generation had already followed the ancient master's footsteps in this matter. Discoursing of the endless succession of generations the pupil says that this "makes the race of fowls eternal; since now the chick and now the egg, in an ever-continued series, produce an immortal species out of individuals which fail and perish. We discern, too, that in similar fashion many lower things rival the perpetuity of higher things. And whether or no we say that there is a soul in the egg, it clearly appears from the cycle aforesaid that there underlies this revolution from hen to egg and from egg again to hen, a principle which bestows eternity upon them. That same, according to Aristotle,[343] is analogous to the element of the stars; and it makes parents generate, makes their semen or eggs prolific, and, like Proteus, is ever present."[344]