Green’s Dictionary of Slang

tallywags n.

also tarriwags, tarrywags
[? SE tally, a notched stick or tail n. (3)]

the testicles; the male genitals.

in S. Butler Posthumous Works in Prose and Verse (1715) 23: Old Harry’s C--piece in the Tower [...] Whose Tarriwags it held long since.
[UK]N. Ward Wandring Spy in Misc. IV 38: Which put his Tarriwags in Pickle, / And made ’em shrink to very little.
[UK]Laugh and Be Fat 5: I would not lose my Tarriwags for the best Dinner in Christendom.
Sublime of Flagellation in Fraxi I 373: He turned about and exhibited his tarriwags [...] She took them in her hand and played with them.
[UK]‘Roger Ranger’ Covent Garden Jester 54: He will certainly geld you; and I dare say he is, he is whetting his knife for the same purpose. [...] I thank thee kindly sweet heart, cried the countryman, are these his tricks with a pox to him – wounds shew me the next way out, for I would not lose my tarriwags for the best dinner in Christendom.
[UK]Grose Classical Dict. of the Vulgar Tongue n.p.: Tallywags, or Tarrywags, a man’s testicles.
[UK]Lex. Balatronicum [as cit. 1785].