Green’s Dictionary of Slang

the testicles.

1594		Gesta Grayorum in J. Nichols Progresses and Processions of Queen Elizabeth (1823) III 326: Capringe Kate, of Clarkenwell, claymes to hold of his Highnes five cunyborowes [...] by night-service, to hold play for five Gentlemen Ushers, each of them with a ferret and two tumblers, weekly.
1661		‘The Character of a Mistris’ in Ebsworth Merry Drollery Compleat (1875) 61: My Mistris is a Conny fine, / She’s of the softest skin, / And if you please to open her, / The best part lies within, / And in her Conny-burrow may / Two Tumblers and a Ferret play.