Dirty minds...

I first read this and laughed my head off. I've heard many a dirty-minded joke, but a dirty-minded riddle? He he he.

Letitia has a large one, and so does cousin Luce.
Eliza has a small one, though large enough for use.
Beneath a soft and glossy curl, each Lass has one in front.
To find it in an animal you at the tail must hunt.

Hermaphrodites have none; Mermaids are minus, too.
Nell Gwynn possessed a double share if books we read are true.
it's used by all in Nuptial Bliss, in Carnal Pleasures found.
Without it Life becomes extinct, the world is but a sound.

Lasciviousness here has it source, Harlots its use apply.
Without it Lust has never been, and even Love would die.
Now tell me what this wonder is, but pause before you guess it.
If you are mother, maid or man, I swear you don't posses it.

The answer isn't the first thing that come to mind... *grin* (Well, unless you're unusually pure-minded that is.)