Green’s Dictionary of Slang

centre of bliss n.

the vagina.

1680		School of Venus 107: What they usually called Loves Paradise and the centre of delight they now in plain English call a Cunt.
1748		Spy on Mother Midnight II 45: Playing twenty wanton Tricks with her delicate Limbs, while I was employ’d rubbing a spot not above an Inch removed from the Center of Delight itself .
1890–1904		Farmer & Henley Sl. and Its Analogues.