You should do the fighters guild quests in oblivion or read 'Infernal City' or read this:
http://www.uesp.net/wiki/Lore:Hist
It's not so clear (as far as I know) what exactly the hist is, some kind of a plant or other lifeform that controls or manipulates the argonians.
The argonians can hear the voice of the hist. I don't know if they must do what the hist says or if it's their free will.
I think if you ask that in the lore section of this forums you get better answers.
But the hist is very important in the attack of Morrowind by the Argonians.