The early Wagner bikes had a frame unlike most others. It mounted the motor very low to the ground, and had a diagonal second bar. It was an interesting concept, but the use of the lower frame tube as an exhaust pipe was used more often that you might imagine. Here is an advert for the 1910 model. Click on the photo to see it and the text larger.
I spotted the remains of a 1912 Wagner hanging on the wall in my friend’s shop. While at the Davenport swap meet he bought it for the rear wheel I believe and just hung the rest of that rusty carcass on a nail to look at. There isn’t much left of the crankcase, but a little bit is remaining at the bottom of the barrel.
Wagners are fairly rare now, but there are a few of them in the midwest. Here is one pic I found. Note that this one has a conventional exhaust pipe.
And Lonnie posted a few more pics here