The Hofner Fledermausguitarre (the Bat Guitar) was a hollow body prototype/exhibition instrument. The vaguely bat-shaped body is 2 inches deep and has an integrated 4 Watt amplifier with loudspeaker, brown suburst finished spruce top, maple sides with ventilation holes.
This was probably the first European guitar with an integrated amplifier - it preceeded the Wandre Krundaal Bikini model. The Bat Guitar was made in very limited numbers in 1960 for the Frankfurt Music Messe (costing 650 DM) but never went into full scale production (probably less than 12 were ever made).
This example, for sale on eBay Germany, has some modifications (the machine heads, bridge and pickguard are replaced) and some damage to the neck and headstock. The seller also says the amplifier and speaker are missing.
The replacement pickguard has been lengthened to cover the holes left when the two amplifier control knobs were removed.
This one has the number 2237 stamped on the top of the headstock.
Sold for 2011 Euros in May 2010.