[azemerov]

I bought a Vivitar 100/3.5 macro lens on eBay. It looks very clean outside, but when I look through the wide open lens pointed slightly aside of bright light source (lamp) I can see some kind of dirt. Here is picture I took from the front of the lens
http://azemerov.fotopic.net/p42052672.html
It looks like this problem is located somwhere inside of the rear lens group. On picture some lines looks like cracks, but in real they aren't - it looks like somebody cleaned lens with dirty rag. Also you can see central spot about 1/2 of diameter - it looks like group of tiny bubbles inside the slightly dimmed glass.
I have no problem with return this lens back, but just for curiosity - what is wrong with this lens? Is it fungus? Or may be two glued lens elements were separated and re-attached again? Does anybody have any clue?

[little laker]

Fungus looks like this

found here
Fungi in Photographic Lens

To me it looks like your lens has somehow gotten some grease on it

If you can return it that's what I'd do.