Larry Niven's much mentioned but rarely read essay Man of Steel, Woman of Kleenex
, online with permission.
All known forms of kryptonian life have superpowers. The same must hold true of living kryptonian sperm. We may reasonably assume that kryptonian sperm are vulnerable only to starvation and to green kryptonite; that they can travel with equal ease through water, air, vacuum, glass, brick, boiling steel, solid steel, liquid helium, or the core of a star; and that they are capable of translight velocities.
What kind of a test tube will hold such beasties?