That Atlas is one cool looking vacuum. Love that paint job!!!
That atlas looks very similar in design to the Tri-star / Compact vacuums. In the tristar, the dirt goes into sort of a paper lined "bucket" instead of a bag. It works the same as a bag in a canister vacuum, except for the fact that the whole top half is open. When it fills up, you lift the round lid, and you take the dirt-filled paper liner out to dispose of it. Tri-stars also have a secondary filter right on the front of the motor, which sits right behind the dirt bucket.