"The Siphonaptera" is a nursery rhyme, sometimes referred to as Fleas.
Big fleas have little fleas,
Upon their backs to bite 'em,
And little fleas have lesser fleas,
and so, ad infinitum.
Sometimes a second verse appears, with lines such as
And the great fleas, themselves, in turn
Have greater fleas to go on;
While these again have greater still,
And greater still, and so on.
The vermin only teaze and pinch
Their foes superior by an inch.
So, naturalists observe, a flea
Has smaller fleas that on him prey;
And these have smaller still to bite 'em,
And so proceed ad infinitum.
Lewis F. Richardson adapted the poem to meteorology, specifically discussing fractal wind patterns:
Big criteria have little criteria,
Upon their backs to bite ‘em;
And little criteria have littler still,
And so on ad infinitum.
- Project Gutenberg (eBook #14353): The Poems of Jonathan Swift, D.D., Volume I (of 2): 
- Standards and Criteria, Journal of Educational Measurement, 1978