Lucretius, De Rerum Natura
William Ellery Leonard, Ed.

     But Centaurs ne'er have been, nor can there be
Creatures of twofold stock and double frame,
Compact of members alien in kind,
Yet formed with equal function, equal force
In every bodily part- a fact thou mayst,
However dull thy wits, well learn from this:
The horse, when his three years have rolled away,
Flowers in his prime of vigour; but the boy
Not so, for oft even then he gropes in sleep
After the milky nipples of the breasts,
An infant still. And later, when at last
The lusty powers of horses and stout limbs,
Now weak through lapsing life, do fail with age,
Lo, only then doth youth with flowering years
Begin for boys, and clothe their ruddy cheeks
With the soft down. So never deem, percase,
That from a man and from the seed of horse,
The beast of draft, can Centaurs be composed
Or e'er exist alive, nor Scyllas be-
The half-fish bodies girdled with mad dogs-
Nor others of this sort, in whom we mark
Members discordant each with each; for ne'er
At one same time they reach their flower of age
Or gain and lose full vigour of their frame,
And never burn with one same lust of love,
And never in their habits they agree,
Nor find the same foods equally delightsome-
Sooth, as one oft may see the bearded goats
Batten upon the hemlock which to man
Is violent poison. Once again, since flame
Is wont to scorch and burn the tawny bulks
Of the great lions as much as other kinds
Of flesh and blood existing in the lands,
How could it be that she, Chimaera lone,
With triple body- fore, a lion she;
And aft, a dragon; and betwixt, a goat-
Might at the mouth from out the body belch
Infuriate flame? Wherefore, the man who feigns
Such beings could have been engendered
When earth was new and the young sky was fresh
(Basing his empty argument on new)
May babble with like reason many whims
Into our ears: he'll say, perhaps, that then
Rivers of gold through every landscape flowed,
That trees were wont with precious stones to flower,
Or that in those far aeons man was born
With such gigantic length and lift of limbs
As to be able, based upon his feet,
Deep oceans to bestride or with his hands
To whirl the firmament around his head.
For though in earth were many seeds of things
In the old time when this telluric world
First poured the breeds of animals abroad,
Still that is nothing of a sign that then
Such hybrid creatures could have been begot
And limbs of all beasts heterogeneous
Have been together knit; because, indeed,
The divers kinds of grasses and the grains
And the delightsome trees- which even now
Spring up abounding from within the earth-
Can still ne'er be begotten with their stems
Begrafted into one; but each sole thing
Proceeds according to its proper wont
And all conserve their own distinctions based
In nature's fixed decree.