Once upon a time...

Another nursery rhyme from one of the kids books entitled Tricky Mindtrap Puzzles

Professor Quantum was telling his young nephew Theory a bedtime story that he himself had enjoyed as a young boy. Unfortunately for Theory, Quantum recalled this popular nursery rhyme from memory—which means it was told in the professor's own words. What rhyme was it?

"Once upon a time there was this ovum, consisting of an envelope of albumen, jelly, and membranes, that decided to moor its entirety on a parapet. Then rather suddenly, and without notice, the ovular being succumbed to a Brobdingnagian gravita­tional pull. The result was that the entire embodiment of the paramount's yeomanry and herbivores were unequal to the task of assemblage."