During the intro to Jeremy there is some sort of guitar harmonic sounding thing, but it sounds huge a bell-like. What is it?

Isn't that Jeff Ament on bass doing the harmonics?

I thought it sounded like bass or guitar harmonics, its just that they're so huge sounding.

Yes is is Jeff Ament.

He has a Hammer 8 string bass (like a 12 string guitar - double courses on each string) With the ocatave strings providing the weird sound.