I THINK jimbo's pic is of a Haskell (basically a Hi-Point under another name), but there are a couple of different companies that made the same basic design.
That strawed screw/plug thing on the Bergmann that you're looking at is part of the magazine system; it holds the spring that operates a lifter arm that forces cartridges up out of a clip so they can be chambered, sort of like a Garand. The ammo (5mm Bergmann) came in little clips of 5 rounds, and you loaded it by swinging down the cover on the right hand side of the pistol (the knurled button at the bottom of the pistol is part of the cover latch/handle), then dropping in a clip and closing the door back up. Here's a shot of what the other side with a clip in place looks like: