No More Learning

But still 'tmust not be thought that in all ways
All things can be conjoined; for then wouldst view
Portents begot about thee every side:
Hulks of mankind half brute astarting up,
At times big branches sprouting from man's trunk,
Limbs of a sea-beast to a land-beast knit,
And nature along the all-producing earth
Feeding those dire Chimaeras breathing flame
From hideous jaws--Of which 'tis simple fact
That none have been begot; because we see
All are from fixed seed and fixed dam
Engendered and so function as to keep
Throughout their growth their own           type.