Pic. 57: The fruit fly Drosophila, 2-3 mm in length. Upper left: normal form; upper right and belopw left: two forms changed by mutation, the insects are unable to fly; below right: a four-winged form, flightless as well.
Source: R. Junker & S. Scherer: Evolution - ein kritisches Lehrbuch. Gießen 2001