Riddle from _The California Voodoo Game_ (Niven/Barnes)

Lelitia has a large one, and so has 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 possesses a double share if books we read are true.
ItŐs used by all in Nuptial Bliss, in Carnal Pleasures found.
Destroy it, life becomes extinct, the world is but a sound...
Lasciviousness here has its sources, 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 donŐt posses it.